The in vitro activity of flucytosine (5FC) against 1,140 clinical isolates of Candida spp. and Cryptococcus neoformans was evaluated and compared with the activity of amphotericin B, fluconazole and itraconazole. Overall, 87.72% (1,000/1,140) of yeasts were susceptible to 5FC. This agent showed less potent in vitro activity against Candida glabrata, Candida krusei, Candida guilliermondii and Cryptococcus neoformans (MIC90s, 8-16 microg/ml) and intermediate activity or resistance to 6.5% of Candida albicans, 5.1% of Candida tropicalis and 0.8% of Candida parapsilosis strains. Amphotericin B showed potent activity against isolates with an MIC of 5FC > or = 8 microg/ml. A total of 112 of 140 strains that were SFC-intermediate or -resistant showed decreased susceptibility to azoles (P < 0.01).