Clinical studies of the new type pivmecillinam tablet (contains 100 mg) was performed on 24 patients with female acute simple urinary tract infections, receiving 300 mg 3 times daily for 7 days orally. Causative organisms in the cystitis cases were isolated singly as E. coli in 18 cases, Staph. aureus in 1 case and Staph. epidermidis in 1 case. From only 1 case with cystitis, E. coli and Staph. epidermidis were isolated mixedly. Clinical efficacy of the new type pivmecillinam tablet was evaluated as excellent in all 21 cases with female acute simple cystitis and 3 cases with female acute pyelonephritis. Side effect was not observed in the all cases.