The effects of exposure to cholesterol in early life on diet-induced hypercholesterolemia in adult rats were investigated. Experiment 1: dams and their offspring received either a control or a cholesterol-enriched diet during gestation and lactation; at 7 weeks of age half of the rats fed each diet were switched to the other diet for 50 weeks. Experiment 2: adult males 6 months old were fed one of the 2 experimental diets for 10 weeks, at which time half of the rats in each group were switched to the other diet for 50 weeks. Cholesterol, triglycerides and phospholipids were determined in liver, serum, heart and aorta at different ages. In both experiments, feeding a cholesterol-enriched diet induced an increase in serum and liver cholesterol and triglyceride levels, but serum phospholipid levels were not influenced by diet. The cholesterol-enriched diet induced a decrease in liver phospholipid levels. Old rats (experiment 2) fed the cholesterol-enriched diet exhibited higher heart cholesterol level than controls. In experiment 1 rats fed the cholesterol-enriched diet in early life and thereafter had lower heart triglyceride levels than the 3 other groups and lower liver triglyceride levels that rats fed control diet in early life and cholesterol diet at 7 weeks. In both experiments, cholesterolemia was not influenced by the diet fed at the beginning of the test. The results indicate that cholesterol given in early life does not protect against diet-induced hypercholesterolemia in adult rats.