Young, weanling rats fed wheat as a sole source of protein have been shown to develop periportal liver lipid infiltration. An attempt has been made to study the mechanism by which these lipid changes are produced. Weanling, male albino rats were fed three diets containing 10% protein based on wheat, wheat fortified with 0.2% lysine or casein, as control. Plasma and liver lipids, incorporation of [1-(14)C]acetate and [U-14C]glucose into hepatic lipids and triglycerides were studied after 6 weeks of feeding. Results of radioactive incorporation studies indicated that hepatic lipogenesis was depressed in rats fed wheat diets. However, adrenal cortical function as well as increased mobilization of lipids from adipose tissue was observed in these rats. Impaired secretion of lipids from liver to plasma is another factor which may be responsible for hepatic lipid accumulation in rats fed the lysine-deficient diet. Rats fed the lysine fortified wheat diet represented a more normal metabolic state though some features of protein deficiency were evident in this group too.