In a search for germline mutations in the DNA mismatch repair genes hMSH2 and hMLH1 in Chinese patients with colorectal cancer we identified a novel missense mutation (V384D) in exon 12 of the hMLH1 gene in 4 out of 26 individuals. This mutation had not been observed in any of 109 German patients who either fulfill the clinical criteria of hereditary nonpolyposis colorectal cancer or had developed colorectal cancer at an early age. In a second series of experiments, DNA samples of 80 healthy. Japanese and 100 healthy Germans were examined for the presence of the V384D mutation. It was observed in 4 Japanese, but in none of the German individuals. Thus, the V384D mutation seems to be confined to the East-Asian population. Since this missense mutation occurs at a less conserved region of the hMLH1 gene, it may represent a nonfunctional polymorphism. However, a role in the pathogenesis of colorectal cancer cannot be ruled out from the present study.