Two distinct strain-related patterns of organism-host interaction on dorsal tongue of immunocompetent rats have been identified for Candida albicans: some isolates induce mucosal lesions, while other isolates penetrate the keratin layer but do not produce a lesion. This study examined the behavior of each of the two types of isolates in a cyclosporin-immunosuppressed rat model. Groups B (normal) and D (cyclosporin) were orally inoculated with a lesion-inducing isolate of C. albicans, while a non-lesional isolate was given to Groups A (normal) and C (cyclosporin). A typical dorsal tongue lesion developed in 4/18 rats in Group B and in 13/16 in Group D (P = 0.00267). No significant difference in infection rate between the normal and cyclosporin-treated animals was seen for the non-lesional isolate. The lack of a host inflammatory response associated with the non-lesional isolate may represent an ecologic advantage for the organism.