T-2588, a new oral β-lactam antibiotic was studied.<BR>For basic evaluation, 4 healthy volunteers were given 100 mg of T-2588 or 250mg of CDX in a cross over manner to determine serum level and urinary recovery. The peak serum level was 0.93μg/ml at 2.5 hrs after administration for T-2588 and 2.58 μ/ml at 2 hrs after administration for CDX, and serum half life was 1.00 hr for T-2588 and 1.55 hr for CDX. The urinary recovery rate within 8 hrs was 28.9% for T-2588 and 83.7% for CDX.<BR>For clinical evaluation, a total of 43 cases comprising 22 patients with acute uncomplicated cystitis, 16 patients with chronic complicated cystitis, 2 patients with chronic complicated pyelonephritis, 2 patients with gonococcal urethritis and 1 patient with acute prostatitis were treated with T-2588, T-2588 was given for 3 to 10 days at a daily dose of 150 to 400 mg with every dose of 50 to 100 mg. The therapeutic effect was assessed according to the drug evaluation criteria for UTI in cases satisfied its conditions and according to judgement of principal investigator in other cases.<BR>The clinical efficacy on 16 cases with acute uncomplicated cystitis was excellent in 10 cases and moderate in 6 cases. Thus, effectiveness rate was 100%. The bacterial eradication rate in such cases was 100%. The clinical efficacy on 9 cases with chronic complicated urinary tract infection was excellent in 4 cases, moderate in 4 cases and poor in 1 case. Thus, the effectiveness rate was 88.9%. Bacteriologically, 19 of 20 strains were eradicated, and the eradication rate was 95.0%. The therapeutic effect in all cases with gonococcal urethritis or acute prostatitis were excellent.<BR>No side effect was noted except for slight hypochondrial pain in 1 case.<BR>The above results and favorable stability against β-lactamases except for cefuroximase suggest that T-2588 is useful as an oral antibiotic for treating urinary tract infection.