A series of 140 patients, undergoing various types of urological endoscopic procedures, was divided into 2 equal, parallel, randomised groups. The first group of 70 patients, undergoing lower urinary tract surgery, was randomised, half to receive norfloxacin prophylaxis and half no antibiotic cover; the other 70 patients, undergoing percutaneous renal surgery, were randomised, half to receive norfloxacin and half cefuroxime. It was found that 26% of patients not receiving antibiotic prophylaxis and 11% on cefuroxime prophylaxis developed post-operative bacteriuria, with a high incidence of urinary tract infection (UTI). Only 1 patient of 70 on norfloxacin prophylaxis developed post-operative bacteriuria, which quickly responded to prolongation of norfloxacin therapy. Prior to surgery, 10% of all patients were found to have previously undetected bacteriuria. This group was at high risk of developing post-operative infection. Norfloxacin effectively prevented post-operative bacteriuria and urinary tract infection in these patients. This study suggests that norfloxacin is a safe and effective prophylactic antibiotic in all forms of urological endoscopic procedures.