Objectives To investigate the epidemiological trend at the late stage of control program and to eradicate filariasis at all Methods Investigation of microfilariae by double slides of thick blood smear of the population in the previous epidemiological area, investigation on vector mosquitoes by the measure to capture and dissect all the fed mosquitoes at once and investigation on serology using IFAT and the method of specific IgG4 detection to detect microfilarial antibody were conducted Surveillance on the movable population included blood examination of microfilariae in people migrating from filariasis epidemic areas, investigation on patients with late stage physical symptom included survey on suspected patients and confirmatory diagnosis made by filariasis control professional workers Longitudinal surveillance included survey on microfilarial rate in 18 natural villages in Changshang, Tancheng, Yicheng, Jiaxiang and Ningyang counties in heary or intermidial epidemic area Infective status of mosquito vector and filarial antibody level of the population were conducted annually at regular interval and at fixed posts for 10 years in succession Results After filariasis was basically eliminated during 1974 to 1980 in 74 counties in the province, 9182 villages in 1587 townships altogether were surveyed and 4?671?078 blood samples were examined By 1996, 3779 cases of them were detected to be microfilarial positive with the microfilarial rate of 0 08% on average In 4137 villages of 714 townships where aetiological positive cases had existed before, 1?430?354 blood samples were collected from the twelfth year after the time of basical elimination, covering 73 8%, 11 7% and 5 0% of the epidemic townships, villages and population, respectively, but no microfilaremial positive patient was found, altogether 690?462 culex pipiens pallens mosquitoes were dissected, 122 of them were found to be positive with the natural infective rate of 0 018%, 274?067 mosquitoes of them were dissected after 1987, but no positive was found And 10?667 cases were tested by IFAT, the positive rate was 1 4%, 2110 cases were detected for IgG4, the positive rate was 0 4%, no microfilarial positive blood slide was found in repeated examinations, 265?596 blood slides from movable population were examinated, the positive rate was 0 055% The survey of local residents showed that new infection did not occur 12?196?191 residents of 50 counties were examinated from 1983 to 1992, 111?207 of them were detected to be cases with physical symptom, with the incidence of 0 92%, and being treated individually For longitudinal surveillance: 80?731 blood samples were examined in surveyed spots, altogether 32 cases with microfilaremia were found which distributed in 14 villages with microfilarial rate of 0 07%-1 15% in each village, the microfilarial density was 1-50?mf/120?μl, Blood microfilaremial positive villages had dropped down to zero as early as from the second to the ninth year All the cases with microfilaremia had converted to negative during the period of 3～6 years in the whole province, the natural infective rate had dropped to zero by the sixth year, and the microfilarial antibody level had declined to the level of unepidemic areas Conclusions This study shows that after basical filariasis elimination, eradication of filariasis could be reached through as soon as possible large scale and repeated surveillance; cleaning upresidual and imported infective sources in time, application of appropriate measures for consolidating the control achievement, combination of longitudinal and cross sectional surveillance Objectives To investigate the epidemiological trend at the late stage of control program and to eradicate filariasis at all Methods Investigation of microfilariae by double slides of thick blood smear of the population in the previous epidemiological area, investigation on vector mosquitoes by the measure to capture and dissect all the fed mosquitoes at once and investigation on serology using IFAT and the method of specific IgG4 detection to detect microfilarial antibody were conducting Survillance on the movable population included blood examination of microfilariae in people migrating from filariasis epidemic areas, investigation on patients with late stage physical symptom included survey on suspected patients and confirmatory diagnosis made by filariasis control professional workers Longitudinal surveillance included survey on microfilarial rate in 18 natural villages in Changshang, Tancheng, Yicheng, Jiaxiang and Ningyang counties in heary or intermidial epidemic area Infective status of mosquito vector and filarial antibody of the population annually in regular province and at fixed posts for 10 years in succession Results After filariasis was basically eliminated between 1974 and 1980 in 74 counties in the province, 9182 villages in 1587 townships altogether were surveyed and 4? 671? 078 blood samples were examined by 1996, 3779 cases of them were detected to be microfilarial positive with the microfilarial rate of 08% on average in 4137 villages of 714 townships where aetiological positive cases had existed before, 1 430? 354 blood samples were collected from the twelfth year after the time of basical elimination, covering 73 8%, 11 7% and 50% of the epidemic townships, villages and population, respectively, but no microfilaremial positive patient was found, altogether 690? 462 culex pipiens pallens mosquitoes were dissected, 122 of them were found to be positive with the natural infective rate of 0 018%, 274067 mosquitoes of them were dissected after 1987, but no positive was found And 10? 667 cases were tested by IFAT, the positive rate was 1 4%, 2110 cases were detected for IgG4, the positive rate was 0 4%, no microfilarial positive blood slide was found in repeated examinations, 265? 596 blood slides from movable population were examinated, the positive rate was 0 055% The survey of local residents showed that new infection did not occur 12? 196? 191 residents of 50 counties were examinated from 1983 to 1992, 111? 207 of them were detected to be cases with physical symptom, with the incidence of 0 92%, and being treated individually for longitudinal surveillance: 80? 731 blood samples were examined in surveyed spots, altogether 32 cases with microfilaremia were found which distributed in 14 villages with microfilarial rate of 0 07% -1 15% in each village, the microfilarial density was 1-50 μmf / 120 μl, Blood microfilaremial positive villages had been dropped to zero as early as from the second to the ninth year All the cases with microfilaremia had converted to negative during the whole of the period from 3 to 6 years in the whole province, the natural infective rate had dropped to zero by the sixth year, and the microfilarial antibody level had declined to the level of unepidemic areas Conclusions This study shows that after after basical filariasis elimination, eradication of filariasis could be reached through as soon as possible as large scale and repeated surveillance; cleaning upresidual and imported infective sources in time, application of appropriate measures for consolidating the control achievement, combination of longitudinal and cross sectional surveillance