Cellulose acetate electrophoresis of serum alkaline phosphatase was done with sera of 45 patients with hepatitis, 47 patients with liver cirrhosis, 48 patients with hepatoma and 6 normal persons. Results demonstrated 4 distinct isoenzyme bands in liver diseases and the most prominent isoenzyme fraction was ey-phosphatase. The presence of the fast liver isoenzyme fraction was more frequent in patients with hepatoma than patients with other liver diseases. Intestinal alkaline phosphatase was observed in a few patients of liver diseases. In hepatoma patients, there was no significant difference in the distributions of alkaline phosphatase isoenzymes according to age, but the presence of the fast liver fraction was commoner in male than female. We concluded that the fast liver isoenzyme fraction was one of the valuable laboratory findings suggesting hepatoma.