The relationship between the ability to secrete a specific acid proteinase (ACP) by Candida tropicalis in the presence of bovine serum albumin as a nitrogen source and virulence for mice was studied using two stable proteinase-positive and proteinase-negative strains (DSY68 and DSY65), which were constructed from the wild-type pathogenic yeast C. tropicalis ATCC 750. The inactivation of the gene encoding the secreted acid proteinase was produced by targeted gene disruption. Mortality rate was slightly lower in groups of mice infected with the proteinase-negative mutant. All other parameters analysed were similar for two strains of yeast. Our results therefore conclude that the ACP secreted by C. tropicalis did not contribute significantly to fungal virulence in systemic infections.