Activities of five urea cycle enzymes, carbamyl phosphate synthetase, ornithine transcarbamylase, argininosuccinate synthetase, argininosuccinase and arginase, were measured in liver of rats fed two types of diet: diet I: raw common corn and, diet II: made of a mixture of corn starch ("maicena"), "chuño (dried potato), sugar and fat. The activities obtained were compared with those of a group of control rats fed a balanced diet with an adequate protein content. Diets were administered after weaning, through an experimental period of 90 days, and enzymatic activities were measured at regular intervals during this time. Animals raised on diet I as well as those raised on diet II, showed low activity of the five urea cycle enzymes, but the decrease of enzymatic activity was more pronounced and appeared earlier in animals raised on diet II. Carbamyl phosphate synthetase and argininosuccinate synthetase, the two synthetases of this cycle, decreased earlier and in a greater degree than the other three enzymes in animals raised on these two types of diet.