Total and protein nitrogen (N) in feces, total N in urine, and food intake were measured in ICR-strain male conventional (CV) and germ-free (GF) mice which were given diets containing 6, 10 or 14% (calculated by N%×6.25) purified whole-egg protein (WE) or crystalline amino acid mixture (AA) with the same amino acid composition as WE, and a protein-free diet. These mice were reared in commercially available plastic cages using chopped filter paper for bedding. In the WE diet group, food intake of CV mice was greater than that of GF mice, but generally, body weight gain and food intake were not changed by the different N sources of the diets in both CV and GF mice, except for a few cases. Food intake per day per 100g body weight was less in the high-N content diet group. Generally, total N of feces per day per 100g body weight in mice fed the WE diet was higher than that of mice fed the AA diet, but there were no differences between CV and GF mice, or among the different dietary N contents. On the other hand, total N excretion in urine in creased according to dietary N content in both CV and GF mice. Total N in urine per day per 100g body weight in CV mice fed the WE diet was higher than that in GF mice. Total N excretion in urine of mice fed the AA diet was higher than that of mice fed the WE diet for both CV and GF mice. The ratio of protein N to total N in feces was higher in CV mice than in GF mice, except for a few cases. The present results show that rearing mice in cages with chopped filter paper for bedding is useful for the separate collection of feces and urine and for measurement of food intake and N metabolism.