Catheter-associated urinary tract infections remain the most common hospital-acquired infection. Regular bacteriologie monitoring of urine from catheterized patients has been advocated as a measure for reducing the morbidity associated with this infection. To assess the effectiveness of this measure we reviewed the records of 100 catheterized patients hospitalized before implementation of a monitoring program and 200 such patients admitted after a daily monitoring program was operational. We found that culturing urine from catheterized patients was infrequent prior to monitoring but, when done, patients usually were febrile, cultures usually were positive, and patients were treated. Monitoring identified more cases of bacteriuria, but less than half of the patients so identified were treated. Being febrile was associated with receiving antibiotics. Infection rates increased with duration of catheterization; long periods of catheterization typically occurred on the neurosurgical, orthopedic, and medical services. Daily bacteriologie monitoring of all catheterized patients is relatively inefficient and does not predictably lead to therapeutic intervention in infected patients. The cost:benefit ratio of this measure might be decreased by applying it to selected patients chosen on the basis of risk factors, including hospital service assignment (Infect Control 1981; 2(3):227-232.)