Serious urinary infections associated with transurethral surgery are a problem of current interest. The underlying causes of their occurrence and the therapeutic approach used are discussed. The study covers 139 patients treated over a two-year period. The types of diseases giving rise to lower urinary tract obstruction and the transurethral operations performed--optic urethrotomy, laser photocoagulation and transurethral resection--are analyzed. In all patients sterile urine assessment is done before, during and after treatment. Identification of the bacterial strains and antimicrobial sensitivity testing are conducted with mini API system--Bio-Merieux, France. The frequency of microbical causing agents and their antibacterial resistance are studied. The tactics in selecting the most adequate drug is discussed. Pseudomonas aeruginosa is identified as urinary infection cause in 49.5 per cent. Good results are obtained in 118 patients (84.9%); among those without urethral catheter prior to operation--97.3 per cent, and in the group with urethral catheter--70.3 per cent. Conclusions are drawn concerning the necessity of microbiological study of the urine in transurethral operations, and undertaking treatment in due course. Retaining of the indwelling urethral catheter prior to intervention should be reduced to a minimum. The clinical efficacy of oral beta-lactams is lower by comparison with fluoroquinolines owing to the multiple resistance of strains. The tenets of picking out an antibiotic for handling significant urinary infections are outlined.