UCP-1 is suggested to have important roles for thermogenesis and energy expenditure. To elucidate whether the A-3826G polymorphism that is located in the 5' flanking region of the UCP-1 gene has roles in healthy young people, the polymorphism was genotyped among 251 young Japanese men whose mean age is 22.7 years old. We analyzed relationship between the A-3826G polymorphism and body mass index (BMI) or six biochemical parameters, serum concentration of total cholesterol (TC), high density lipoprotein (HDL) cholesterol, triglyceride (TG), asparatate aminotransferase (AST), alanine aminotransferase (ALT), fasting plasma glucose. The genotype frequencies were observed at the frequencies of 24.3% for AA, 48.2% for AG and 27.5% for GG, respectively. When BMI and the biochemical parameters were compared by ANOVA among individuals with each genotype, the statistical difference was observed only for BMI (P=0.016). Bonferroni's test demonstrated that the men with the AG genotype have higher BMI than those with the AA genotype (22.4+/-2.8 vs. 21.4+/-2.2) (P=0.04). The individuals with the AG genotype also showed trend to have higher BMI than those with the GG, although the difference was not statistically apparent (22.4+/-2.8 vs. 21.5+/-2.3) (P=0.07). Our results indicated that the young healthy Japanese men with the AG heterozygote showed higher BMI than those with other genotypes.