objective: To assess the efficacy and toxicity of orally administered itraconazole in the treatment of nonmeningeal, nonlife-threatening forms of blastomycosis and histoplasmosis. design: Prospective, nonrandomized, open trial. setting: Multicenter trial at 14 university referral centers. patients: Eighty-five patients with culture or histopathologic evidence of blastomycosis (48 patients) or histoplasmosis (37 patients). Patients receiving other systemic antifungal therapy were excluded. interventions: Itraconazole was administered orally at doses of 200 to 400 mg/d. Patients in whom treatment was considered a success were treated for a median duration of 6.2 months (blastomycosis) and 9.0 months (histoplasmosis). Disease activity was assessed at baseline; drug efficacy and toxicity were evaluated at monthly intervals during therapy, and efficacy was evaluated at regular follow-up visits after completion of therapy. The median duration of posttreatment evaluation for successfully treated patients was 11.9 months (blastomycosis) and 12.1 months (histoplasmosis). measurements and main results: Among the 48 patients with blastomycosis, success was documented in 43 (90%). The success rate for patients treated for more than 2 months was 95% (38 of 40). Among the 37 patients with histoplasmosis, success was documented in 30 (81%). The success rate for patients treated for more than 2 months was 86% (30 of 35). All patients with histoplasmosis in whom treatment failed had chronic cavitary pulmonary disease. Toxicity was minor, only 25 (29%) patients experienced any side effects, and itraconazole toxicity necessitated stopping therapy in only 1 patient. conclusions: Itraconazole is a highly effective therapy for nonmeningeal, nonlife-threatening blastomycosis and histoplasmosis. The drug is associated with minimal toxicity. © 1992.