The relationship of smoking, alcohol use, body mass index, and physical activity to glucose tolerance was studied in 2407 male self-defense officials aged 49-56 years who received a health examination before retirement at the Self-Defense Forces Fukuoka Hospital from October 1986 to December 1990. Body mass index (BMI) was significantly, positively related to impaired glucose tolerance (IGT) and noninsulin-dependent diabetes mellitus (NIDDM); after adjustment for rank of the Self-Defense Forces, smoking, alcohol use, prior diagnosis of diabetes mellitus, and parental history of the disease, odds ratios (ORs) of IGT and NIDDM for the highest (> or = 25.5 kg/m2) versus lowest (< 21.6 kg/m2) quintile of BMI were 4.2 [95% confidence interval (CI) 2.6-6.8] and 4.6 (95% CI 2.3-9.3), respectively. Cigarette smoking was weakly, positively associated with IGT and strongly so with NIDDM; adjusted ORs of IGT and NIDDM for 800 cigarette-years or more versus never smoking were 1.6 (95% CI 1.1-2.5) and 4.1 (95% CI 1.8-9.3), respectively. The prevalence of IGT and NIDDM tended to be decreased among men with high physical activity as measured by the time spent for vigorous exercise in leisure time. There was virtually no association between alcohol consumption and either IGT or NIDDM. The findings suggest that obesity and cigarette smoking are important factors in the development of glucose intolerance in middle-aged Japanese men.