ABSTRACT The somatomedin (SM) activity was measured in blood samples withdrawn simultaneously from hepatic (HV) and peripheral (PV) veins in 10 adult patients without liver disease (control group) and in 18 alcoholic patients with cirrhosis. SM activity in the control group was 1.27 ± 0.18 U/ml (mean ± sem) in the HV and 1.00 ± 0.17 U/ml in the PV. In patients with cirrhosis the SM activity was respectively 0.50 ± 0.05 and 0.56 ± 0.06 U/ml. SM activity was greater in the normal subjects than in the cirrhotic patients (P < 0.001 when SM activity measured in the HV, and P < 0.01 when measured in the PV). Close examination of the means of differences of SM activity between the HV and PV, showed that the differences were significantly different from 0 in control only (P < 0.02). At least, this difference (0.275 ± 0.093 U/ml) is greater (P < 0.01) than the one observed in cirrhotic patients (0.066 ± 0.036 U/ml). In 16 subjects, the hepatic blood flow was measured, and the mean hepatic SM activity production was estimated to be 398 ± 334 U/min in 6 subjects from the control group, and 16 U/min in 10 patients with cirrhosis. The difference is significant (P < 0.01). The relationship between SM activity, biochemical liver function parameters, hepatic blood flow and immunoreactive growth hormone were also studied. The results confirm that the liver is involved in serum somatomedin activity generation.