Background: Nitric oxide is continually released from normal skin and has antimicrobial effects. An acidified nitrite cream releases supraphysiologic concentrations of nitric oxide and is fungicidal in vitro. Objective: The purpose of this study was to assess the efficacy of an acidified nitrite cream as treatment for tinea pedis. Methods: Sixty patients were recruited with both a clinical diagnosis of tinea pedis and hyphae identified on direct microscopy; they were randomly placed into an active group treated with twice-daily application of a mixture of 3% salicylic acid in aqueous cream and 3% nitrite in aqueous cream for 4 weeks and a control group treated with 3% salicylic acid in aqueous cream and aqueous cream alone. Nineteen patients completed the trial in the active group and 16 patients in the control group. Mycologic cure (negative results on microscopy and culture) and clinical improvement were measured at 0, 2, and 4 weeks and after a 2-week interval with no treatment. Results: At the end of the treatment period, 18 of the 19 patients in the active group were mycologically cured as were 11 of 16 in the control group (p = 0.042). Two weeks after the cessation of treatment, 13 of 19 patients in the active group were mycologically cured and 5 of 16 in the control group (p = 0.028). The initial clinical scores in the active and control groups were 8.1 and 8.19 (two-tailed p = 0.95). At 4 weeks they were 1.66 and 6.0 (two-tailed p = 0.002) and after 2 weeks with no treatment 1.45 and 7.4 (two-tailed p < 0.0002). Conclusion: Acidified nitrite is effective therapy for tinea pedis. (J Am Acad Dermatol 1998;38:559-63.)