Although Escherichia coli accounts for as many as 50 per cent of nosocomial urinary tract infections, the most problematic of these infections are usually caused by Klebsiella, Pseudomonas, and Proteus. Patients in whom infections with these pathogens are most likely to develop are described. Empiric antibiotic therapy is discussed as it relates to coverage of potential infecting pathogens. The development of antibiotic resistance is illustrated with specific examples from a Cleveland hospital regarding resistance of E. coli to ampicillin and of Pseudomonas to gentamicin. The importance of becoming familiar with hospital sensitivity and resistance patterns is stressed.