In order to more clearly define the influence of adipocyte size and plasma cholesterol on adipose tissue cholesterol storage, hypercholesterolemia was induced in male Fisher rats at a time when body weight and adipocyte size become fixed. In one experiment (experiment 1), increasing amounts (0, 0.05, 0.5 and 5.0%) of dietary cholesterol were added to a fat-free, purified diet (sucrose-casein-cellulose) fed to 1 year old virgin males. In experiment 2, retired breeder rats were fed 0 or 5% cholesterol, with and without corn oil supplementation of the purified diet. The plasma cholesterol responses (in experiment 1) to the various dietary cholesterol levels were in the order 0 = 0.5 greater than 0.05 greater than 5.0% = stock diet. In experiment 2, however, rats fed cholesterol had higher plasma cholesterol values than those fed the cholesterol-free diet. When total cholesterol concentration per 10(6) adipocytes was examined in four adipose depots, it was found that adipocyte cholesterol content tended to increase with increasing levels of circulating total cholesterol, regardless of the cholesterol content of the diet. The accretion of cholesterol in adipocytes was accompanied by enhanced storage in the esterified form, a response very similar to that of liver in these experiments but unlike skeletal muscle. It is concluded that adipose tissue participates physiologically in the response to hypercholesterolemia in the rat, but that the response may depend upon the nutritional or metabolic state of the animal prior to cholesterol feeding (young rats versus retired breeders) and is not similar in all adipose tissue depots.