Twenty patients with chronic oral candidiasis were assigned by random allocation to a two-week course of either 10-mg clotrimazole buccal troches or placebo taken five times daily in a double-blind clinical trial. Each of the 10 recipients of clotrimazole had marked regression of symptoms and mucosal lesions, and in nine patients potassium hydroxide preparations and cultures of mucosal scrapings gave no evidence of candidiasis. In contrast, only one of the 10 patients receiving placebo showed any improvement. The clinical outcome in the clotrimazole-treated group was significantly more favorable (P less than 0.001) than in the group receiving placebo. No adverse reactions to the drug were observed. After the blind phase of their trial, 15 patients were treated with clotrimazole troches in an open trial. One to three troches per day were found adequate to sustain remissions. We conclude that clotrimazole is highly effective treatment for chronic oral candidiasis.