In this study the in vitro activity of ofloxacin, pefloxacin and ciprofloxacin against various gram negative bacteria isolated from urinary tract infections was examined. Of 80 isolates (24 E. coli, 10 Enterobacter, 10 Klebsiella, 23 Proteus, 10 Pseudomonas, 2 Morganella and 1 Serratia) 49 were from inpatients, and 31 were from outpatients. Ciprofloxacin was the most potent compound and no resistant strain was found against ciprofloxacin, while 1 Enterobacter strain and 1 Pseudomonas strain were found to be resistant to both ofloxacin and pefloxacin. Another Pseudomonas strain was resistant to pefloxacin only. All of the resistant bacteria were from nosocomial infections.