Voriconazole (CAS 137234-62-9, UK-109,496), a new antifungal triazole derivative, was studied in vitro against 650 clinical isolates, representing yeasts, moulds and dermatophytes, and was compared with fluconazole (CAS 86386-73-4), amphotericin B (CAS 1397-89-3), and griseofulvin (CAS 126-07-8). The mean minimum inhibitory concentrations (MICs) of voriconazole were 0.06 microgram/ml against yeasts (n = 187), 0.74 microgram/ml against moulds (n = 260) and 0.10 microgram/ml against dermatophytes (n = 203). Data from these in vitro studies showed that voriconazole was more potent than fluconazole against most species studied, but particularly against the isolates of moulds and dermatophytes. Overall, voriconazole and amphotericin B indicated comparably good activity against yeasts and moulds. Voriconazole was highly potent against 13 Aspergillus species studied (mean MIC 0.35 microgram/ml) and also showed noteworthy activity (mean MICs 0.08-0.78 microgram/ml) against emerging and less common clinical isolates of opportunistic moulds such as of Alternaria spp., Cladosporium spp., Acremonium spp., Chrysosporium spp., and Fusarium spp. In addition, voriconazole was more active in vitro than griseofulvin against most dermatophytes tested. The in vitro results confirmed that voriconazole has indeed a broad antifungal spectrum and could also be effective against a wide range of fungal infections in patients.