From March, 1990 to February, 1992, we administered fluconazole as antifungal prophylaxis at doses of 3-5 mg/kg/day to 40 patients with prolonged and severe neutropenia following intensive chemotherapy. Fungemia was observed in 3 out 40 patients, and all three of them were due to Candida non-albicans strains: two Candida parapsilosis and one Candida guilliermondi. In vitro sensitivity tests showed that all three isolated strains were susceptible to amphotericin. In one case, Candida guilliermondi was tested for sensitivity to fluconazole and found to be resistant. We conclude that fluconazole prophylaxis proved effective in preventing Candida albicans infections, but it could also contribute to the emergence of Candida non-albicans strains. It might be possible that fluconazole at higher doses could prevent the selection of less susceptible Candida strains.