Two apparently healthy male groups, one 60 (n = 67) and one 50 (n = 367) years of age were compared with respect to blood glucose, serum lipid and serum insulin concentration and intravenous glucose tolerance. These groups were recruited from two health surveys performed on male populations of these ages in the municipality of Uppsala. The prevalence of diabetes mellitus in the two health survey populations were 4.5% and 0.9%, respectively. No significant differences in serum triglycerides, serum cholestrol and fasting serum insulin concentrations were found between the two age groups. Significantly higher k-values and higher early serum insulin response to i.v. glucose were found in the younger than in the older age group. The older age group was more obese, than the younger group. It is concluded that the prevalence of diabetes increases considerably in males between 50 and 60 years of age. In parallel, the prevalence of decreased glucose tolerance is increasing, which might partly be explained by increased body weight and partly by an impaired pancreatic beta-cell function.