Abstract The green alga Scenedesmus acutus was cultivated in clean water on a pilot-plant scale, and after harvest it was drum dried at 120°C for 5–8 sec. The drum-dried alga was fed ad lib. to weanling albino rats as the sole protein source at protein levels of 10 or 15% in the diet for 12 wk. Control rats were given diets containing 10% casein. Treatment at either dietary level did not result in any harmful histological or haematological effects. Urine analyses did not indicate any abnormalities in any of the treated groups. Liver cholesterol levels were lower in animals given the algal diets than in the controls while serum cholesterol levels were similar in the treated and control groups. The activities of the hepatic enzymes succinic dehydrogenase and alanine aminotransferase in the treated groups were similar to those in the controls. Gel electrophoresis did not show any major differences between the serum proteins of the test animals and those of the controls.