Aztreonam is a monobactam antibiotic active against aerobic gram-negative bacteria. The susceptibility of 127 urinary tract isolates to aztreonam, cefotaxime, cefonicid and ceftazidime was determined. Aztreonam showed good antibacterial activity even against Pseudomonas spp. Only 7 bacterial strains were resistant to aztreonam. The clinical efficacy and pharmacokinetics of aztreonam were assessed in two patients treated for urinary tract infections. The concentrations of aztreonam in serum and urine are reported. Aztreonam safety was evaluated on 20 patients given aztreonam immediately prior to an elective abdominal, urinary or gynecological operation. The results provide support for the use of aztreonam for prophylaxis.