The effect of propylthiouracil (PTU; 300 mg/day) on alcoholic liver disease was evaluated in 133 patients in a short-term randomized double-blind trial. Severity of the disease was assessed by a composite clinical and laboratory index (CCLI). A normalization rate (NR) representing the improvement rate in CCLI was calculated. Patients with alcoholic hepatitis, with and without cirrhosis, showed a significantly higher NR on PTU (43.6 .+-. 4.6) than on placebo (19.8 .+-. 3.3; P < 0.001). A similar effect was observed in patients with abnormal prothrombin (no biopsy): NR was 32.9 .+-. 6.9 on PTU and 2.6 .+-. 3.7 on placebo (P < 0.005). The effect of PTU on each clinical and laboratory component of the CCLI was compared in these 2 groups. In 38 patients with alcoholic hepatitis and in 25 with abnormal prothrombin, those on PTU showed a greater improvement in 15 of 15 items (P < 0.001) and 14 of 15 (P < 0.01), respectively. When patients were divided according to the severity of the disease into those in the lower and upper halves of the CCLI range (81 and 52 patients, respectively), PTU had a significant effect only in the latter; the NR was 41.4 .+-. 3.8 on PTU and 22.5 .+-. 4.2 on placebo (P < 0.005). PTU was ineffective in patients with inactive cirrhosis.