Terbinafine has previously been shown to be highly active against dermatophytes and many other filamentous fungi. However, its activity against yeasts is controversial, with earlier reports suggesting that it has low activity, while more recent studies demonstrated that terbinafine is effective against yeasts. In this study, the in vitro activity of terbinafine was evaluated against a broad range of fungal isolates. We examined the susceptibility of 100 yeast strains (10 species including Candida albicans, non-C. albicans, fluconazole-susceptible and -resistant candidal strains), and 184 strains of filamentous fungi and dermatophytes (29 species including Aspergillus, Fusarium, Sporothrix, Trichophyton rubrum, T. mentagrophytes, T. tonsurans, Microsporum canis and Epidermophyton floccosum), using the NCCLS M27-A microdilution methodology for yeasts and a modified M38-P methodology for moulds. The endpoint for terbinafine was defined as 80% inhibition compared with the growth control well. The mean yeast and filamentous fungi minimum inhibitory concentration values +/- SEM (in microg ml(-1)) for terbinafine were: 6.60 +/- 0.73 and 1.04 +/- 0.28, respectively. In conclusion, our data suggest that terbinafine, in addition to its potent activity against dermatophytes, is considerably effective against a broad range of yeasts and filamentous fungi in vitro. Therefore, investigations concerning its antifungal activity in vivo against such organisms should be pursued.