An infection of Trichophyton mentagrophytes was induced in 13 dogs, and of Microsporum canis, in 9 dogs. After the lesions became established, they were assigned to a group for clotrimazole treatment, miconazole treatment, or no treatment. Treatments were applied one daily for 28 days, using a double blind method. The lesions were evaluated by daily scoring of severity and by semiweekly culturing throughout the treatment period. Compared with untreated controls, the response to clotrimazole was significantly better from day 11 until the end of the study. The response to clotrimazole equaled or occasionally exceeded that to miconazole.