Chemosensitivity of hepatocellular carcinoma tissues from 72 patients to 6 antitumor agents was assayed using the succinate dehydrogenase inhibition test. Sensitivity was positive in 47.2% of tissues exposed to adriamycin, 53.5% to mitomycin C, 10.3% to 5-fluorouracil, 51.5% to cisplatin and aclacinomycin A. respectively, and 52.9% to carboquone. Eight percent of the tissues were sensitive to all 6 drugs, while the resistance rate to all drugs was 36.5%. The remaining 55.5% were sensitive to only some of the drugs. When a comparison of the sensitivity to the 6 drugs was made between two different areas of tumors in 16 patients, positive or negative sensitivity was in a range of 76.9-92.9%. The hypovascular masses seen on the angiography and the histologically well differentiated tumors were resistant to adriamycin, a drug most commonly prescribed to treat patients with liver cancer. For some of these tumors, mitomycin C or carboquone may be effective. Our observation shows that the succinate dehydrogenase inhibition test is useful for determining which drugs will be effective for a particular tumor.