Alpha-methyldopa-induced histologic alterations were investigated in 21 patients with hepatic injury after short- and long-term exposure. Seven patients developed liver injury within 6 months and 24 after several years (mean, 5 years) of exposure. Histologic findings and clinical and biochemical data differed significantly in the two groups. Morphologic analysis of the short-term-treated group revealed marked parenchymatous degeneration, focal, confluent and massive necrosis, and inflammation. Fatty accumulation and increased fibrous trabeculae were characteristic for the patients treated for long term. All patients in the short-term-exposed group had acute and severe hepatitis. Four of them had icterus. Two patients died of hepatic coma. Patients in the long-term-treated group had for several months initially mild but increasing discomfort, dyspepsia, nausea, and colics. Liver function tests in these groups revealed differences in serum albumin, bilirubin, and transferase levels. No changes were observed in alkaline phosphatase and Thrombotest. Fat accumulation and fibrous trabeculae suggest that the alterations precede the clinical symptoms and biochemical signs of hepatitis. The findings show that alpha-methyldopa may induce hepatocellular injury after short- and long-term exposure.