To assess the incidence of cyclosporine A-induced hepatotoxicity, we retrospectively analyzed liver biochemical test results in 59 patients with endogenous uveitis who received cyclosporine A. All patients had normal liver tests before treatment and had at least six determinations during a 6- to 36-month course of therapy with cyclosporine A at a dose of 2-10 mg/kg/day. Thirty-four (58%) patients developed at least one abnormality of liver tests, and 19 (32%) had a prolonged pattern of abnormalities. The usual abnormalities consisted of a mild, transient increase in alkaline phosphatase levels occasionally accompanied by slight elevations in serum bilirubin and aminotransferase activities. Peak alkaline phosphatase levels ranged from 125 to 243 units/liter and persisted for seven days to 48 months. Thus, biochemical evidence of mild cholestatic liver injury was common in patients receiving cyclosporine A. These abnormalities are usually self-limited and asymptomatic but may cause diagnostic difficulty if a preexisting liver disease is present.