Efficacy and safety of cefadroxil, a new oral cephalosporin, were compared with that of cephalexin in the treatment of 28 women with acute urinary tract infections. According to a randomized double-blind design, each patient received cefadroxil 1,000 mg. twice daily or cephalexin 500 mg. four times a day for ten days. Cures based on urine culture five to nine days post-treatment were obtained for all but 1 patient receiving cefadroxil; reinfection after eradication of the original pathogen was recorded for only 1 patient in each treatment group. No drug-related side effects or significant clinical laboratory abnormalities were observed during the study. Cefadroxil 1,000 mg. given twice daily was as effective and as well tolerated as cephalexin 500 mg. given four times daily. The significance of this dosage schedule advantage is discussed.