We measured the plasma transforming growth factor-beta (TGF-beta) concentration in 14 patients with human hepatocellular carcinoma (HCC) and 9 age-matched normal subjects using growth inhibition assay of mink lung epithelial cells. The calculated plasma TGF-beta concentration in the patients with HCC was 28.6 +/- 27.9 ng/ml (mean +/- SE), showing significant elevation compared with that in 9 normal subjects (5.3 +/- 3.3 ng/ml, P less than 0.01). In three cases, we could measure plasma TGF-beta levels before and after their treatment for HCC. The plasma TGF-beta levels decreased from 59.0 to 18.2 ng/ml after hepatic resection in one case, and from 24.0 to 10.7 ng/ml and from 12.4 to 3.4 ng/ml after transhepatic arterial embolization in the other two cases. These data indicate that plasma TGF-beta level is elevated in patients with HCC, probably due to release from HCC tissues.