From July 1997 to June 1998, a total of 1323 subjects, including 1180 controls, 94 patients with diabetes mellitus, and 49 patients with deep-vein thrombosis, varying in age and gender, were consecutively entered into our study. Their mean (+/- SD) age was 50.0 +/- 18.0 years, range 1-99 years; 930 were male and 393 were female. None of the subjects was found to have abnormal prothrombin 20210A allele mutation. In total, 150 subjects (11.3%) were found to have a homozygous 677 C-->T mutation of the methylenetetrahydrofolate reductase gene, in which 125 were controls (10.6%), 17 were diabetics (18.1%) and 8 were patients with deep-vein thrombosis (16.3%). However, 524 subjects (39.6%) were found to have a heterozygous methylenetetrahydrofolate reductase 677 C-->T mutation. We suggested that the Chinese race dose not have the prothrombin 20210A allele, but can carry the 677 C-->T mutation of the methylenetetrahydrofolate reductase gene.