Eugenol and vanillin were examined for in vitro antifungal activity against the medically important yeasts, Candida albicans and Cryptococcus neoformans. Minimal inhibitory concentrations (MIC) and minimal fungicidal concentrations (MFC) were determined for each compound against 31 strains of C. albicans and 33 strains of C. neoformans. With eugenol, the mean MIC's for C. albicans and C. neoformans were 625 and 293 micrograms/mL, respectively, while the mean MFC's were 1209 and 521 micrograms/mL, respectively. With vanillin, the mean MIC's for C. albicans and C. neoformans were 1250 and 738 micrograms/mL, respectively, while the mean MFC's were 5000 and 1761 micrograms/mL, respectively. With C. albicans, inhibition and retardation of growth were similar for yeast and mycelial forms, but germ tube formation was inhibited at concentrations lower than those which inhibited growth. Short-term toxicity tests with mice using the intraperitoneal route gave maximum tolerated doses of 62.5 mg/kg for eugenol and 125 mg/kg for vanillin and excluded their use as therapeutic agents for systemic mycoses.