One hundred and four pathogenic yeast isolates (32 Candida albicans, 20 Candida tropicalis, 20 Candida parapsilosis and 32 Cryptococcus neoformans) and 21 mould isolates (13 Aspergillus spp. and eight Fusarium spp.), most of which were isolated from patients with cancer, were tested for susceptibility to free amphotericin B and a small unilamellar liposomal formulation of amphotericin B using a microbroth dilution method. Minimal fungicidal concentrations were also determined for Candida spp. and Cryptococcus neoformans. The minimal inhibitory concentrations of liposomal amphotericin B were comparable with those of the free drug; furthermore, the fungicidal activity of these two drugs did not differ significantly.