The expression of secreted aspartyl proteinases (Saps) by clinical isolates of Candida albicans, C. tropicalis and C. parapsilosis in human saliva supplemented with glucose and in a proteinase-inducing medium (YCB-BSA), was investigated. Also, yeast growth, pH fluctuation and total protein concentration of the saliva cultures during incubation were measured. Sap expression was assessed by evaluating the enzyme activity as well as the antigen concentration. Saps were expressed well in human saliva supplemented with glucose by all three Candida species, although greater expressions was found in YCB-BSA medium. C. albicans isolates were significantly more proteolytic than the non-albicans isolates. In general, for all three species, the rate of yeast growth, pH fluctuation and percentage reduction of total salivary protein concentration concurred with the degree of expression of Saps. These data strongly suggest that Saps of C. albicans, C. tropicalis and C. parapsilosis may play an active role in the progression of oral candidoses, particularly with regard to the abundance of low pH microenvironments in the oral cavity, which are regularly replenished with dietary carbohydrates.