The alcohol dehydrogenase (ADH; alcohol: NAD+ oxidoreductase: EC22.214.171.124) activity was measured and restriction mapping about the Adh region was performed to assess DNA polymorphism in Drosophila melanogaster populations of Korea in 24 iso-second chromosome lines: 10 lines from the Chunan population and 14 lines from the Pusan population. The mean ADH activity in AdhF lines was 3.5 fold higher than that of AdhS lines. The mean ADH activity in the Chunan population was higher than that of the Pusan population. Polymorphism due to both restriction site presense/absence and insertion/deletion was detected. One restriction site polymorphism, 2 kinds of insertions, and 3 kinds of deletions were observed. It was concluded that DNA polymorphism in the Adh DNA region is present in Korean populations of Drosophila melanogaster. The overall heterozygosity in Korean populations of Drosophila melanogaster was 0.843. A strong linkage disequilibrium between BamHI (- 7.0) and Adh allotype and between D-2 deletion and Adh allotype was observed. This suggests that the mutation occurred in Adh alleles on a chromosome lacking the BamHI (- 7.0).