Out of 75 patients in whom nosocomial infection of the urinary tract occurred following operation for disturbance of micturition 43 (57.3%) suffered clinically manifest inflammatory complications, however only in 26 cases (34.6%) was this germ the cause. In the remaining 17 cases there were superinfections. From these results it is concluded that the isolated Providencia stuartii strains were not very virulent. In cases of asymptomatic providencia-bacteriuria the authors consider specific antibacterial therapy to be indicated only if the excretion of germs does not cease spontaneously after micturition has been restored to normal.