To evaluate the role of portal blood flow in severe acute hepatitis leading to the formation of ascites, we studied the portal blood flow of 30 patients with severe acute hepatitis (20 without ascites and 10 with ascites), 20 patients with mild acute hepatitis and 20 healthy normal volunteers using duplex sonography. The portal blood flow of patients with severe acute hepatitis and ascites (421 +/- 94 mL/min) was lower than that of the volunteers (725 +/- 131 mL/min), the mild acute hepatitis (658 +/- 148 mL/min), and the severe acute hepatitis (633 +/- 108mL/min) without ascites (P < 0.001). The congestion index of severe acute hepatitis and ascites (0.16 +/- 0.04 cm.s) was higher than that of the volunteers (0.09 +/- 0.03 cm.s, P < 0.001), the mild acute hepatitis (0.09 +/- 0.02 cm.s, P < 0.001), and the severe acute hepatitis (0.12 +/- 0.04 cm.s, P < 0.02) without ascites. Portal blood flow was negatively correlated with prolonged prothrombin time (P < 0.001) and serum total bilirubin level (P = 0.002) and congestion index was positively correlated with heart rate (P = 0.006), prolonged prothrombin time (P < 0.001) and serum total bilirubin level (P = 0.001). Our study shows that in severe acute hepatitis, portal blood flow was reduced in patients with ascites. The non-invasive ultrasonic Doppler is a safe and helpful method in the clinical evaluation of portal hypertension in severe acute hepatitis.