As volume changes are a typical finding in the two-kidney, one-clip hypertensive rat model (2K1C), it is of interest to investigate within what time frame these volume changes occur and their relation to hypertension. Kidney volume changes in Wistar rats were measured by three-dimensional (3D) ultrasonography (USG). Clipped induced stenosis was applied to the left renal artery in 11-wk-old animals (n = 8), using age-matched nonclipped rats as controls (n = 7). Ultrasonographic recordings were made before clipping and, thereafter, weekly with corresponding systolic blood pressure and body weight measurements. The nonclipped kidney showed increased volume at week 2, 5 and 7. Three wk after clipping, clipped kidneys were smaller than the nonclipped kidneys (0.47 +/- 0.11 mL versus 1.28 +/- 0.07 mL). No difference was found between the left and right kidney in the control group at any week. Blood pressure was significantly higher in the 2K1C hypertensive group 4 weeks after clipping (201 +/- 16 versus 139 +/- 4 mm Hg) with stable blood pressure thereafter. Three-dimensional USG showed that clipping caused a decrease in kidney volume from week 3 in the clipped kidney and a volume increase in the nonclipped kidney at week 2. A significant increase in blood pressure appeared after week 4.