There are relatively few antifungal agents available for the treatment of systemic mycoses. The incidence of these infections, particularly among the immunocompromised, has increased significantly in recent years. Amphotericin B, flucytosine and the azole-derivatives--fluconazole, itraconazole and ketoconazole--are the only drugs of value in the treatment of systemic yeast infections currently available. To date resistance among individual yeast species or strains has only been a serious problem with flucytosine. However, resistance among Candida spp. to orally administered azole-derivatives has been observed. The frequency with which resistance has been described in clinical practice among yeasts differs considerably between the three azole antifungal agents. Fluconazole has been implicated in emergent resistance more frequently than ketoconazole, and ketoconazole more often than itraconazole. It must be a matter for concern that, by analogy with the known emergence of antibiotic-resistance among bacteria, that the widespread use of a drug inactive against a particular species may lead to an increased incidence of such infections. An international epidemiological survey is required to establish the extent and degree of resistance to the azole antifungals.