1. The specific radioactivity of [14C]cholesterol in plasma and in serial biopsies of muscle and skin was measured in Rhesus monkeys for 156 days after a single intravenous injection of [14C]cholesterol.
2. Analysis of the specific radioactivity—time curves in terms of a two-compartment system indicated that all the cholesterol of muscle is exchangeable with the plasma cholesterol and that local synthesis does not contribute significantly to the cholesterol in muscle.
3. Analysis of the curve for specific radioactivity of skin cholesterol suggested the presence of a small pool of cholesterol with slow turnover. A contribution to skin cholesterol from local synthesis could not be excluded.