The effects of aging on the relationships between changes in body weight, serum lipid levels (total cholesterol, HDL-cholesterol, triglyceride, beta-lipoprotein), and blood pressure (systolic pressure, diastolic pressure) were studied. The subjects were 17,689 Japanese (aged 19 to 88 years) who had received annual examinations at health centers for two consecutive years. After the date were adjusted for sex, body mass index, and serum lipid levels at baseline, changes in serum lipid levels and blood pressure per kilogram change in body weight were estimated for 3 age groups (under 45, 45 to 64, and 65 or older). Positive relationship between changes in body weight and blood pressure were noted for all 3 age groups. Although total cholesterol, triglyceride, and beta-lipoprotein levels all decreased with weight loss in the under-65 groups, total cholesterol in the 65-and-over group did not change significantly. The increases in total cholesterol, triglyceride, and beta-lipoprotein levels were associated with weight gain in the under-65 groups, but not in the 65-and-over group. HDL-cholesterol levels in all age groups decreased significantly with weight gain. These results suggest that aging affects the relationship between changes in body weight and serum lipid levels but not that between changes in body weight and blood pressure.