A clinical trial was designed for evaluation of the efficacy, safety, and patient tolerance of cefoxitin. Of 26 patients who could be evaluated clinically, 21 had respiratory tract infections; all but one patient responded satisfactorily to therapy with cefoxitin. There were no adverse systemic reactions, nor was any renal or hematologic toxicity noted. In two instances levels of hepatic enzymes became slightly elevated; these changes were possibly related to administration of cefoxitin. About one-third of patients receiving cefoxitin developed minor local reactions at the site of intravenous administration; however, there was only a single instance of true thrombophlebitis. Results of this study suggest that cefoxitin is a safe and well-tolerated antibiotic that is efficacious in therapy of acute respiratory tract infections caused by bacteria that are sensitive to this drug.