Clinical background was investigated on 913 bacterial strains isolated from patients with urinary tract infections (UTIs) in 11 hospitals during the period from June, 1992 to May, 1993. 1. Distribution of sex, age and infections Among over forties males, the majority was taken by complicated urinary tract infections. Among females, the uncomplicated urinary tract infections was most frequent without a relation of age. 2. Distribution of sex, age and pathogens isolated from UTIs IN uncomplicated UTIs, Escherichia coli was most frequently isolated without a relation of age, and next CNS in under fifties. In complicated UTIs without indwelling catheter, E. coli and Enterococcus faecalis were isolated with a frequency of 12-28%, respectively. In complicated UTIs with indwelling catheter, Pseudomonas aeruginosa were most frequently isolated, and next E. faecalis. 3. Administration of antibiotics and pathogens isolated from UTIs In uncomplicated UTIs, pathogens, after administration of antibiotics, isolated from patients have obviously decreased from 306 to 44 isolates. And also, pathogens of complicated UTIs without indwelling catheter, have decreased from 217 to 76 isolates. However, in complicated UTIs with indwelling catheter, pathogens after or before administration of antibiotics, were not revealed an obvious change. 4. Pathogens and UTIs with or without factor and operation In uncomplicated UTIs with or without factor and operation, E. coli was mainly detected. In complicated UTIs without indwelling catheter and with or without factor and operation, E. coli was mainly detected. In complicated UTIs with indwelling catheter and with factor and operation, P. aeruginosa and E. faecalis were detected, 19.6% and 16.0%, respectively. Without factor and operation, P. aeruginosa was detected, 28.9%, and next E. faecalis 13.3%. The distribution of pathogens after administration of antibiotics was similar.