The relationship between the urometrogram and the indwelling ureteral catheter was studied on female dogs having surgically explanted bladders. A new monitoring technique was employed which allowed for simultaneous recording of urometrogram, spurt volume, wave speed, and wave geometry for each peristaltic wave. The caliber of the catheter was shown to influence both contractile amplitude and basal pressure level of the ureter. In one case, an increase in catheter size from 3.6 Fr. to 5 Fr. resulted in a 5-mm Hg rise in basal pressure with a simultaneous increase of 35 mm Hg in peak pressure amplitude. In addition, it was also shown that in dog ureters, catheters as small as 3.6 Fr. may result in elevated pressure levels. Based on experimental observations and an understanding of the passive and contractile characteristics of ureteral smooth muscle, a new model ofthe urometrogram is presented which is based on a contact pressure between the ureteral wall and catheter.