The serum concentrations of alpha-fetoprotein were measured by radioimmunoassay technic in 72 patients with primary hepatoma, 39 patients with other liver diseases and 28 patients with other various malignant cancers including 12 patients with liver metastasis and were compared with those in 30 normal adults. The following results were obtained: 1) The serum AFP concentrations in normal adults were in a range 0 to 86 IU/㎖ with a mean value of 16.2±10.7 IU/㎖. 2) 72 patients with primary hepatoma showed serum AFP concentrations in a range of 28 to over 4000 IU/㎖, 68 patients(94.4%) and 57(79.2%) patients with greater than 100 IU/㎖ and 400 IU/㎖ respectively. 3) In the 44 patients with primary hepatoma, serum AFP concentrations higher than 400 IU/㎖ was noted in 94.1% of serum HBs Ag positive patients and in 62.9% of HBs Ag negative ones, which showed statistically significant difference in serum AFP concentrations in regard to the occurrence of HBs Ag. 4) Liver scanning showed a cold area in 56(91.8%) of 61 patients with primary hepatoma, there was no significant difference in serum AFP positivity (AFP>400 IU/㎖) in presence of cold area on liver scan. 5) Pathological classification of 21 patients with primary hepatoma were 19 of hepatocellular carcinoma and 2 of cholangiocellular carcinoma, all patients with hepatocellular carcinoma were serum AFP concentrations higher than 400 IU/㎖, but 2 cholangiocellular carcinoma were lower than that.