AbstractAdult rats were fed diets containing 0, 25, 50, 100, 200, or 400 g lactalbumin/kg diet for 10 days, and the activities of six cecal microbial enzymes were determined. Total activity per cecum of azoreductase,β‐glucosidase, and urease increased significantly with increasing dietary protein, whereas the activities ofβ‐glucuronidase and nitroreductase were not significantly affected. Nitrate reductase activity decreased significantly. Total numbers of cecal bacteria were not significantly altered by the treatment.