A prospective 19-month study of 26 human immunodeficiency virus type 1-infected patients with episodes of erythematous or pseudomembranous oral candidiasis was done to evaluate the significance of Candida albicans biotypes in patients treated with antifungal therapy. Changes in the biotype of C. albicans were frequently noted in recurrent oral candidiasis. However, no correlation was found between the various biotypes and the clinical features of oral candidiasis, the clinical stage of human immunodeficiency virus type 1 infection, or the number of CD4+ lymphocytes. On the contrary, a significant correlation appeared among clinical lesion features, CD4+ cell numbers, and time of clinical disappearance of the oral lesions. Changes in the biotype of C. albicans were observed at the end of the antifungal therapy in 17 of 26 patients who had a second appearance of oral candidiasis as well as in 10 of 14 subjects who experienced a third reappearance of oral candidiasis.