Diethylphosphono acetic acid (DPA) was used as a current hapten to generate broad specificity polycolonal antibodies against a group of organophosphorus pesticides. Six New Zealand white rabbits were immunized with immunogens synthesized by the active ester method (AEM) or 1-ethyl-3-(3-dimethylaminopropyl)-carbodimide method (EDC). The titers of antisera reached 25 600 by AEM and 6 400 by EDC,respectively. Polyclonal antibodies raised against DPA were screened and selected for the competitive indirect enzyme-linked immunosorbent assay (CI-ELISA). A CI-ELISA for DPA was developed with a detection limit of 3.536 ng mL-1 and an I50 value of 0.182 μg mL-1. The assay specificity was evaluated by obtaining competitive curves for several structurally related compounds as competitors. The antiserum showed high affinities to chlorpyrifos,diazinon,omethoate,parathion-ethyl and profenofos with I50 of 0.12,0.15,0.21,0.88,0.97 and 2.5 μg mL-1,respectively. The results indicate that the assay could be a screening tool for quantitation and semi-quantitation determination of the above former five organophosphorus pesticides. Diethylphosphono acetic acid (DPA) was used as a current hapten to generate broad specificity polycolonal antibodies against a group of organophosphorus pesticides. Six New Zealand white rabbits were immunized with immunogens synthesized by the active ester method (AEM) or 1-ethyl-3- (3-dimethylaminopropyl) -carbodimide method (EDC). The titers of antisera reached 25 600 by AEM and 6 400 by EDC, respectively. Polyclonal antibodies raised against DPA were screened and selected for the competitive indirect enzyme-linked immunosorbent assay (CI- ELISA). A CI-ELISA for DPA was developed with a detection limit of 3.536 ng mL-1 and an I50 value of 0.182 μg mL-1. The assay specificity was evaluated by obtaining the competitive curves for several structurally related compounds as competitors. The antiserum showed high affinities to chlorpyrifos, diazinon, omethoate, parathion-ethyl and profenofos with I50 of 0.12,0.15,0.21,0.88,0.97 and 2.5 μg mL-1, respectively. The results indicate that the assay coul d be a screening tool for quantitation and semi-quantitation determination of the above former five organophosphorus pesticides.