The production of proteases by Candida albicans in batch cultures of human saliva supplemented with glucose was investigated with two clinical strains of Candida and both individual and pooled samples of whole saliva from volunteers. Salivary proteolysis during a 48-h period was estimated by biochemical and isoelectric focusing techniques. Candidal growth in saliva was associated with acid production and salivary proteolysis and there was a highly significant positive correlation between these two activities. Neither candidal growth nor proteolysis was observed in glucose-free control samples and with one strain of Candida cultured in the saliva of one individual. Isotachophoretic analysis of culture liquor showed a significant increase in acetate and pyruvate ions. The oral cavity provides niches that have a low pH and are periodically supplemented with dietary carbohydrates. The acidic proteases of C. albicans may play a role in the pathogenesis of oral candidoses.