The possible adverse effects of chronic, high-dose fluconazole therapy are detailed from analysis of a multicenter, dose-escalating study of the therapy of invasive mycoses. Ninety-three adult patients were studied, 48 of these received > 6 months therapy and 20 received > 1 year. Fifty-eight patients received > 300 mg/day, and 7 received > 600 mg/day. One patient received 1,997 g over 86 months. Twenty-seven percent experienced possible symptomatic side effects, which resulted in 2 patients discontinuing therapy, and 42% had asymptomatic laboratory abnormalities, none of which were progressive. Headache, hair loss and anorexia were the most common symptoms experienced (each by 3% of patients), and eosinophilia and aspartate aminotransferase increases were the most common laboratory findings (12 and 10%, respectively). Fluconazole appears well tolerated and safe in these doses and durations.