Fluconazole is very effective in the treatment of oral thrush, but an increasing number of patients with recurrent oropharyngeal candidiasis have developed fluconazole-resistant yeasts following repeated courses of fluconazole therapy. Fluconazole resistance can develop in a single persistent strain of yeast, but more commonly fluconazole resistance results from emergence of a different Candida albicans strain or another Candida species. Higher doses of fluconazole are more effective against resistant strains in murine candidiasis, but the utility of identifying resistant isolates and treating resistant yeasts with high doses of fluconazole is not established. Thus, the objectives of this proposal are to define prospectively the epidemiology of fluconazole-resistant oropharyngeal candidiasis, to correlate therapeutic response with fluconazole resistance, and to evaluate the role of higher doses of fluconazole in treating resistant yeasts. These objectives will be achieved by longitudinally evaluating patients with HIV infection/AIDS treated with fluconazole for recurrent oropharyngeal candidiasis. The goal of these studies is to improve the treatment of oropharyngeal candidiasis in patients with HIV infection/AIDS. The specific aims of this proposal are: 1) To longitudinally evaluate a cohort of patients with recurrent oropharyngeal candidiasis for the development of fluconazole resistance and to correlate that resistance with clinical response to therapy; 2) To establish strain identity using molecular characterization of the yeasts in order to establish the epidemiology of fluconazole- resistant oropharyngeal candidiasis; 3) To correlate antifungal susceptibility testing with clinical outcome and to determine the utility of screening susceptibility techniques to detect fluconazole resistant yeasts; 4) To evaluate high doses of fluconazole against resistant yeasts in a murine model of candidiasis; 5) To determine the clinical utility of high doses of fluconazole in treating patients with fluconazole-resistant yeasts.