The hybrid clone FD1 constructed by fusion of Chinese hamster cell line Wg3-h with human lymphocyte was irradiated with X-ray. Fourteen survival clones were isolated and 3 of them, F5B, F52B, F61A were analyzed in detail by cytogenetic and biochemical methods. The results of chromosome Gbanding followed by Giemsa-11 differential staining show that there exists a deleted human chromosome 4 in all of the three hybrids. This deletion of human chromosome 4 in F61A is 4pter→4q21. The results of isozyme analysis of phosphoglucomutase-2 (PGM2) which is located on 4p14→4q21 confirm our cytogenetic conclusion. We used polyaerylamide gel electrophoresis to study the alcohol dehydrogenase (ADH) in human lymphocyte, Wg3-h and hybrid clones. Their electrophoretic pattern showed that human ADH isozyme did express, in the peripheral blood lymphocyte, hybrids FSB, F52B, F61A and FD1. According to these results, we suggest that one of the Class 1 ADH structural genes is located on the human chromosome 4pter→4q21. Rec The hybrid clone FD1 constructed by fusion of Chinese hamster cell line Wg3-h with human lymphocyte was irradiated with X-ray. Fourteen survival clones were isolated and 3 of them, F5B, F52B, F61A were analyzed in detail by cytogenetic and biochemical methods. The results of chromosome Gbanding followed by Giemsa-11 differential staining show that there exists a deleted human chromosome 4 in all of the three hybrids. This deletion of human chromosome 4 in F61A is 4pter → 4q21. The results of isozyme analysis of phosphoglucomutase-2 (PGM2) which is located on 4p14 → 4q21 confirm our cytogenetic conclusion. We used polyaerylamide gel electrophoresis to study the alcohol dehydrogenase (ADH) in human lymphocyte, Wg3-h and hybrid clones. Their electrophoretic pattern showed that human ADH isozyme did express, in the peripheral blood lymphocyte, hybrids FSB, F52B, F61A and FD1. According to these results, we suggest that one of the Class 1 ADH structural genes is located on the human chromos ome 4pter → 4q21. Rec