We conducted a two-center dose ranging study to evaluate the efficacy, tolerance, and toxicity of cefpimizole, a new cephalosporin, in the treatment of uncomplicated gonorrhea in 96 males. Twelve patients at each center were treated intramuscularly with single doses of 1.0, 0.5, 0.25, and 0.125 g of cefpimizole. All urethral infections were cured at the highest dose, but lower doses produced progressively decreasing cure rates of 90% (0.5 g), 83% (0.25 g), and 71% (0.125 g). Treatment failures of rectal and pharyngeal infections occurred at the highest dose level. Geometric mean MICs for cefpimizole for successfully and unsuccessfully treated volunteers were 0.088 and 0.282 μg/ml, respectively. A prominent adverse effect was clinically significant pain at the injection site, which occurred in 57 (59%) of 96 patients. Results of the study demonstrate that cefpimizole offers no advantage over currently available antibiotics in the treatment of uncomplicated gonorrhea in men.