OBJECTIVE Naftifine HCl 2% cream (NAFT-2%) is a topical allylamine antifungal preparation under development in the U.S. The objective of this randomized, double-blind, vehicle-controlled study was to evaluate the efficacy and safety of a two-week course of once-daily NAFT-2% vs. vehicle in the treatment of Tinea cruris ("jock itch"). METHODS A total of 334 subjects with T. cruris were enrolled and randomly assigned to NAFT-2% (n=166) or vehicle (n=168), which was applied once daily for 14 days. Efficacy and safety were evaluated at week 2 (end of treatment) and week 4. Efficacy measures included complete cure, treatment effectiveness, mycological cure, clinical cure, and clinical success and were analyzed only in subjects with a positive potassium hydroxide (KOH) and dermatophyte culture at baseline (n=75, naftifine; n=71, vehicle). Safety was assessed by adverse events and changes from baseline in clinical status and laboratory studies. RESULTS At week 4, 25 percent of naftifine-treated subjects achieved complete cure vs. three percent of vehicle subjects and 72 percent achieved mycological cure vs. 16 percent of vehicle treated subjects (one-sided, P<0.001). Treatment effectiveness was achieved in 60 percent of NAFT-2% subjects vs. 10 percent of vehicle subjects (one-sided, P<0.001). Clinical cure rate and clinical success rate were 33 percent and 84 percent in NAFT-2% subjects, respectively vs. 10 percent and 46 percent in vehicle subjects (both P is less than 0.001, 2-sided). Week 2 efficacy response rates in NAFT-2% subjects were all lower than at week 4 but were significantly higher than week 2 vehicle-treated counterparts (P<0.025). Treatment-related AE occurred in 11 subjects (7 NAFT-2%, 4 vehicle) during the study. The most common AE in both groups were contact dermatitis (2 NAFT-2%), pruritus (2 vehicle), and application site reaction (1 per group). CONCLUSION NAFT-2% applied once daily for two weeks (one-half the treatment duration for naftifine 1% cream) is efficacious and safe for the treatment of T. cruris.