Thirty human immunodeficiency virus-positive patients carrying Candida albicans in their oropharynx were treated with fluconazole and were monitored for 90 to 570 days. Fluconazole-resistant C. albicans (MIC, > 32 micrograms/ml) appeared only in seven patients and only after 90 days of treatment corresponding to a total dose of more than 10 g. Resistance was not associated with resistance to other azole derivatives. Susceptible and resistant strains from each patient had the same genotype (as defined by electrophoretic karyotype and restriction fragment length polymorphism). Thus, the resistant strains were selected by the antimycotic treatment from the susceptible strain present in each case.