The in vitro antifungal activities of itraconazole and its active hydroxyl metabolite, hydroxy-itraconazole (R 63372), against Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans were compared by visual assessment of growth as well as by colorimetric MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide] assay using microtitre plates containing four different media. Minimum inhibitory concentration (MIC) end points determined by the colorimetric MTT assay correlated well with those obtained by visual assay. The two drugs showed different MIC values depending on the medium used. The activity of itraconazole was equal to or greater than the activity of hydroxy-itraconazole against most of the fungi tested. Both drugs showed lower MIC values against A. fumigatus and Cr. neoformans in brain heart infusion broth (BHI) medium than in yeast nitrogen base (YNBG) medium, Sabouraud glucose broth (SAB) or "synthetic amino acid medium, fungal" (SAAMF). However, the MIC end point of these drugs against C. albicans in BHI and SAB media was difficult to determine visually as well as by MTT assay. In C. albicans, the MTT assay method using SAAMF and YNBG media is recommended for the determination of MICs.