Renal vasoconstriction commonly occurs in decompensated liver cirrhosis and is entirely reversible after hepatic transplantation. In this study we evaluated by Doppler ultrasonography the changes of renal vascular resistance occurring during the first month after transplantation. In 16 cirrhotic patients the intrarenal resistive index at the level of interlobar arteries and the blood urea nitrogen and serum creatinine levels were measured before (range, 1 to 34 days) and after transplantation (days 1, 3, 7, 14, 30). Before transplantation the median resistive index value was 0.69 (95% CI, 0.65 to 0.71) and eight of 16 patients showed abnormal values (0.70 or more). After transplantation, the median resistive index was significantly decreased on all the evaluation days, and no patient had abnormal values on posttransplantation day 7. No significant correlation was found between resistive index and serum creatinine or blood urea nitrogen levels. Doppler ultrasonography is a simple tool to evaluate the recovery of normal intrarenal arterial resistance levels after liver transplantation. One week appears to be the optimal timing to evaluate the renal resistive index in the posttransplantation period.