We investigated the effect of urinary tract infection on bladder and renal pelvic urodynamics in a rat model to examine the role of pressure during infection. Either an antibiotic solution (control group) or Escherichia coli with type 1 pili (infected group) was instilled into the bladder. After 2 to 6 days simultaneous continuous bladder and renal pelvic pressures were measured during urinary flows from less than 2 to greater than 20 ml./kg. per hour while the bladder filled and emptied. Bladder pressures from 50 to 100% of maximum capacity and maximum voiding pressures were significantly higher in the infected group than the control group (36.7 +/- 6.79 cm. water versus 25.5 +/- 5.21 cm. water, respectively, p less than 0.0001). Renal pelvic pressures were significantly higher in the infected group during bladder filling at all urinary flows examined and actually exceeded bladder pressure for the highest flows. We conclude that elevated renal pelvic pressures may contribute to renal changes observed during urinary tract infection.