The diagnosis of an urinary tract infection (UTI) is proved by the identification of a significant leucocyturia and bacteriuria of the mid-stream urine analysis in men and catheter urine in women. A diagnostical localisation is possible by the case history as well as clinical, sonographical and laboratory tests (leucocytes, CRP) to classify into a cystitis and infection of the parenchyma, respectively an uncomplicated or complicated UTI. Untreated complicated urinary tract infections have a bad prognosis. The therapy consists of bed rest, normalization of the urinary flow, a specific antibiotic therapy corresponding to the antibiotic sensitivity pattern and the administration of a prostaglandin-synthesis-inhibitor. Every physician should choose one of the many antibiotics and must get acquainted with the pharmacokinetics and side-effects. In severe acute infections, a calculated antibiotic therapy in certain combinations is necessary until the bacteriological findings are known. Corresponding to the spectrum of bacteria in complicated UTI, one should select a fluoro-chinolone, a broad-spectrum penicilline in combination with a beta-lactamase-inhibitor, a cephalosporine of the second and third generation with a relative stability against beta-lactamase as well as an aminoglycoside. Reserve-antibiotics for special indications are for example, cefsulodine. Less effective than the drugs mentioned above is cotrimoxazole, which was favourized before. In complicated UTI, the older gyrase-inhibitors like nalidixic acid, pipemidic acid, cinoxacin and nitrofurantoin are not longer indicated. There is only one indication for the application of doxycyclin: the treatment of bacterial prostatitis. A lower dosage of antibiotics and a drug therapy of 7-10 days are sufficient.(ABSTRACT TRUNCATED AT 250 WORDS)