In man, ornithine carbamyl transferase is localized mainly in the liver and to a lesser extent in the smll intestine. Because of these findings, one might expect damage only to the liver or perhaps the small intestine to cause elevated ornithine carbamyl transferase activity in serum $(_S-OCT)$. Serum ornithine carbamyl transferase activity was determined in thirty normal subjects, and fifteen patients with viral hepatitis and fifteen patients with liver cirrhosis. The correlation of $_S-OCT$ with $_S-GPT$ and $_S-GOT$ was studied. The mean $_S-OCT$ activity in thirty normal Korean subjects was $0.094{pm}0.043$I.U./L of serum. Elevated $_S-OCT$ activity was observed in patients with liver disease. The correlation coefficient was 0.18 for $_S-OCT$ and $_S-GPT$, ana 0.40 for $_S-OCT$ and $_S-GOT$.