Female rats were prematurely weaned on the 18th postnatal day to a high fat (HF) or high carbohydrate (HG) diet. Twelve days later they were all given free access to a cereal based stock diet. When aged 10 months, they were all fed an atherogenic diet for the next 2 months and were then killed. Blood cholesterol levels were higher in the HG group at 11 months but not 1 month later. After 2 months of feeding the atherogenic diet, injected 14C-cholesterol disappeared more slowly from the HF group during the first 24 hours after injection but more rapidly during the next 48 hours than the HG group. At that time, serum glucagon levels in the HF group had doubled but remained unchanged in the HG group. Serum insulin levels decreased significantly during that same period in the HF group but not the HG group. Consequently, the I/G molar ratio was lower in the HF than the HG group after 2 months of feeding the atherogenic diet. At 12 months, selected enzyme activities in white adipose tissue and liver did not differ between the two groups, except for phosphoenolpyruvate carboxykinase, the activity of which was higher in the HG