Protein from many sources show negative correlation between their biological values and the levels of urea in the blood or urine of rats or pigs. On the basis of the difference in protein quality between raw and heated soybeans, it would be predicted that there should be a higher level of urea in the blood and urine of rats fed raw soybean meal. In the present study, however, little or no difference in the levels of urea in the blood and urine of animals fed raw or autoclaved soybean meal could be demonstrated. It is postulated that the increased catabolism of the poor quality protein of raw soybeans may be masked by a concomitant depression of liver arginase activity and/or a decrease in the total quantity of amino acids available for catabolism because of lower digestibility of the raw soybean protein.