The acute systemic haemodynamic effects of cigarette smoking are well known, but there are no studies dealing with the possible smoke-related acute changes of splanchnic circulation in man. In the present study we evaluated the acute effects of cigarette smoking on portal blood flow (PBF) in normal subjects by the use of Doppler ultrasound. Twenty-three normal volunteers were asked to smoke two cigarettes with a known total nicotine content (1.1 mg each) in a supine position. Each cigarette was smoked during a 5 min period and a 5 min interval between the two cigarettes was allowed. Both mean PBF velocity and volume were evaluated at time 0 (basal values) and 8, 15, 30, 45 and 60 min after the first inhalation of the first cigarette. The basal mean PBF velocity (22 cm/s; 95% CI 20.9-24.2) was significantly decreased at 8 min (19 cm/s; 95% CI 17.9-20.8; P < 0.0007) and 15 min (20 cm/s; 95% CI 17.8-21.3; P < 0.005). Similarly, the PBF volumes at 8 min (710 mL/min; 95% CI 660-876; P < 0.002) and 15 min (750 mL/min; 95% CI 650-862; P < 0.005) were significantly lower than those measured at time 0 (850 mL/min; 95% CI 766-987). Both mean PBF velocity and volume measured at successive times did not differ significantly from basal values. The present study shows that cigarette smoking causes acute and transient reduction of PBF velocity and volume in normal subjects.