The present study was carried out with the aim of comparing the microbiological and clinical efficacy of norfloxacin, cinoxacin and aztreonam in urinary tract infections. Patients were tested who had infections of the higher and/or lower urinary tracts associated with complicating factors. The microorganism most frequently isolated in these individuals was Escherichia coli. The assays carried out with the aim of testing the in vitro antibacterial activity (agar diffusion method and minimum inhibitory concentration) on the microorganisms responsible for the infections, as well as the evaluation of clinical efficacy, showed that norfloxacin has a wider antibacterial spectrum of action and inhibitory activity greater than the other two drugs tested.