To study the possible involvement of candidal adherence in mucosal colonization, we examined the in vitro adherence capabilities of seven Candida species. Adherence was evaluated by direct microscopic examination and by a quantitative radiometric adherence test. The results indicate that C. albicans adheres to vaginal and buccal epithelial cells to a significantly greater degree (P less than 0.01) than the other species tested. C. tropicalis and C. stellatoidea demonstrated moderate adherence capabilities, while C. parapsilosis adhered only to a slight degree. Other species failed to interact with isolated mucosal cells. These findings suggest that there is a relationship between the adherence capabilities of the Candida species and their abilities to colonize mucosal surfaces, since those species which adhere are those which most frequently colonize mucosal surfaces. C. albicans was found to be adherent under a variety of environmental conditions. Stationary-phase blastospores of C. albicans were found to be more adherent than logarithmic-phase yeasts, and larger blastospore cell-to-epithelial cell ratios resulted in greater adherence values. The actual number of adherent yeasts varied considerably when epithelial cells were obtained from different donors.