Groups of 5–8 baboons were fed either a control or hypercholesterolaemic diet for 6 months. During the last 90 days, each group was given 5 i.v. injections of bovine serum albumin (BSA) at 16 day intervals or control injections of saline. Only those animals which were both hypercholesterolaemic and injected with BSA developed aortic and coronary atherosclerosis.