In three series of experiments hypercholesterolemia was induced in male Sprague-Dawley rats by a 3% cholesterol-enriched diet. The development of hypercholesterolemia was considerably retarded when 20% Scenedesmus powder was incorporated in the diet. In animals fed with standard diet and cholesterol for 6–8 weeks, the average concentration of blood plasma cholesterol increased from 2.0 to 3.6 mmol/l. In contrast, the final concentration reached only 2.4–2.8 mmol/l in animals receiving the cholesterol diet with algae. The plasma cholesterol level in animals receiving only an algal diet did not appear to be influenced. The mean value at the beginning of the test was 2.0 and 2.2 mmol/l at the end. The level of plasma triglyceride in animals fed on algae with and without the addition of cholesterol was lower than that of the controls. The algae-enriched diet prevented an excessive deposition of cholesterol in the liver. The increase in weight of the livers of rats receiving the cholesterol-enriched standard diet and the cholesterol-enriched algal diet were 2.0 and 0.8 g, respectively. The cholesterol content of the livers increased to 600 and 180 mg, respectively.