14 patients with hepatocellular carcinoma and one with a hepatoblastoma were given AFP antibodies and changes in serum AFP levels and clinical courses were observed. Anti-human AFP horse IgG was purified by immunoadsorbent column chromatography. 1 mg of the purified antibody was able to bind 100-150 micrograms of AFP. 200-800 mg were given to each patient, according to their AFP levels. Also, conventional anti-cancer agents were administered consecutively. In all cases, the serum AFP levels measured by RIA decreased rapidly to undetectable levels within 24-48 h after the infusion. Then, in seven of 15 cases, the relatively low level was maintained for periods of 10-96 weeks. In the remaining eight cases, the serum AFP level increased again after 1-2 weeks and rose further with clinical deterioration. Since the antibody administered was undetectable in the serum within 2 weeks after its infusion, it is suggested that the AFP antibody had an inhibitory effect on the production or the release of AFP in some patients.