Fifty female Sprague-Dawley rats were divided into five groups of 10 animals and were given a low concentration (0.01%) of tetracycline in drinking water. Four of the groups were orally inoculated weekly with the yeast Candida albicans for a period of 25 weeks. Each group received a different strain. Three of the four strains of yeast were consistently recovered upon culture of the oral cavity during the course of the study. Two of the strains produced grossly visible lesions (four of 10 and two of 10 animals) on the midline dorsal tongue, whereas no lesions were seen in the other two experimental groups or the control group. Clinical findings were supported histologically. These data suggest definite strain-related differences in mucosal pathogenicity for the lingual mucosa of rats among the strains of C. albicans studied.