An alpha‐fetoglobulin was found in the sera of 35 out of 48 patients with histologically proved primary liver cell carcinoma (72.9%). The sera of normal healthy persons, of patients with diseases other than primary liver cell carcinoma, and of patients with cholangiocarcinoma were all negative for alpha‐fetoglobulin. Thirty‐three sera from 11 patients with hepatoma were alpha‐fetoglobulin negative by double well diffusion method, of which 30 were further proved to be alpha‐fetoglobulin positive when reassayed by a more sensitive single well radial diffusion method. This fetoprotein appeared more frequently in female or cirrhotic patients with hepatoma than in male or non‐cirrhotic patients. No obvious correlation between alpha‐fetoglobulin and histologic picture, or liver function study or clinical course of hepatoma was evident. Quantitatively, the alpha‐fetoglobulin varied from one patient to another, and, in the same individual, it increased with the growth of hepatoma. The serum level of alpha‐fetoglobulin was scarcely changed by chemotherapy. However, it would disappear or decrease in titer 1 to 3 weeks after resection of hepatoma‐bearing lobe and keep increasing in titer or reappear if hepatoma recurred or metastasized.