The effect of brown rice with low protein intake was studied in five healthy young men. Feces were weighed, the digestibility of nutrients was determined, and blood tests were made. Each subject followed a diet consisting mainly of polished rice for 14 days and one consisting mainly of brown rice for 8 days. Both diets contained 0.5 g protein per kg of body weight. The brown rice diet had 3 times as much dietary fiber as the polished rice diet. On the brown rice diet, fecal weight increased, and apparent digestibility of energy, protein, and fat decreased, as did the absorption rates of Na, K, and P. The nitrogen balance was negative on both diets, but more negative on the brown rice diet. The phosphorus balance on the brown rice diet was significantly negative, but other minerals were not affected by the diet. The levels of cholesterol and minerals in the plasma were not significantly different on the polished rice diet and the brown rice diet. Comparing these results with data on standard protein intake (Miyoshi, H. et al (1986) J. Nutr. Sci. Vitaminol., 32, 581-589.), we concluded that brown rice reduced protein digestibility and nitrogen balance.