The purpose of this study was to investigate the difference between species (mouse and rabbit) and the effect of hypercholesterolemia on the ability of their peritoneal macrophages to release unesterified cholesterol to an exogenous acceptor. The macrophages from mouse, normocholesterolemic rabbits and hypercholesterolemic rabbits (Mm, Mnr, Mhr) were loaded with cholesterol esters by incubation with oxidatively modified low density lipoprotein or plasma lipoprotein (beta-migrating very low density lipoproteins). When human HDL was used as cholesterol acceptor for 24 h of incubation, the Mm Cells, the Mnr cells and Mhr cells retained about 40%, 70%, and more than 90% of their cholesterol esters. The difference between species of lipoproteins were not effective for the ability to release cholesterol esters. ACAT (acylcoenzyme A: cholesterol acyltransferase) inhibitor 58-035 increased these capacities. These data suggest that the limited capacity of macrophages from hypercholesterolemic rabbits to release cholesterol may be related to the progression and resistance to regression of atherosclerosis, and that ACAT activity might influence this capacity.