We determined whether the synthesis and degradation of N-acetylglutamate would regulate urea synthesis when the ornithine status was manipulated. Experiments were done on two groups of rats, each being treated with ornithine or saline (control). The plasma concentration of urea and the liver concentration of N-acetylglutamate in rats given ornithine were each significantly higher than in the control rats. Compared with the control rats, the liver N-acetylglutamate degradation was significantly lower in those rats treated with ornithine. Treatment of the rats with ornithine did not affect N-acetylglutamate synthesis in the liver. An inverse correlation between the liver N-acetylglutamate degradation and liver concentration of N-acetylglutamate was found. These results suggest that the lower degradation of N-acetylglutamate in the ornithine treatment group would be likely to increase the hepatic concentration of this compound and stimulate urea synthesis.