Cimetidine has been shown to reduce liver blood flow, as measured by indocyanine green clearance, in normal subjects. Concern over the potential deleterious effects of such reduction in cirrhosis led to the measurement of blood flow in 14 cirrhotics receiving oral or intravenous cimetidine. Liver blood flow was measured by the clearance of galactose at steady state during infusion of 40 mg per min. In six patients receiving 300 mg cimetidine by mouth each 6 hr for 4 days, basal flow (1,019 ± 186 ml per min) was not significantly altered by cimetidine (1,087 ± 156 ml per min). Intravenous infusion of cimetidine (300 mg) did not significantly alter flow in five patients betwen the basal (1,096 ± 334 ml per min) and treatment periods (1,051 ± 383 ml per min). Hepatic extraction of galactose in three patients (82 ± 19%) was not significantly altered by cimetidine infusion (81 ± 13%). The failure to reduce liver blood flow with cimetidine in this population may be due to their diminished proportion of portal venous flow, or alternatively suggests that histamine is not an important modulator of flow via H2 receptors. At a clinical level, the use of cimetidine in this population can continue without fear of further reduction in liver blood flow.