Antitumor effect and reduction of tumor size by some cytokines as Biological Response Modifier have been demonstrated by various studies. Endogenous tumor necrosis factor is produced from macrophage. To increase the antitumor effect of transcatheter arterial embolization (TAE) in hepatocellular carcinoma (HCC), we treated 7 HCC patients with endogenous tumor necrosis factor (ETNF) which was induced by hepatic arterial injection of gamma-IFN (1.0-3.0 X 10(6) IU) as priming agent and OK-432 (2-5 KE) as triggering agent. TAE was performed with Lipiodol, ADM and gelatin sponge on 3-10 days after the induction of ETNF. TNF activity was detected in 2 cases and suspected to depend on the dose of gamma-IFN and OK-432. Serum alpha-Fetoprotein levels after the injection of ETNF began to decrease from 3-30 days in 5 patients and remained unchanged in 2 cases. Serum alpha-Fetoprotein levels after TAE with the induction of ETNF were decreased 1-5 months in 5 cases. Reduced size and low-density area on CT scan in 3 advanced cases after these procedures were no different from those of HCC patients treated with TAE alone. In one of two inoperable cases with a single mass lesion in the liver, CT scan after one more added TAE following these procedures showed a low-density area around the Lipiodol uptaking tumor, indicating obstruction of the peripheral portal vein. CT scan of another case revealed low density around Lipiodol in the tumor, which showed complete necrotic change. In all cases, middle-grade fever and hypotension were seen transiently, but these subsided by symptomatic treatment. The antitumor effect of TAE in HCC might be enhanced with ETNF induced by hepatic arterial injection of a low dose of gamma-INF and OK-432.