Spinal cord injury (SCI) at Th13 was induced in female Wistar rats, and changes in the urinary bladder were examined during the acute phase of SCI. Wet weights of the spinal bladders increased twofold over controls by 7 days after SCI. Intravesical volumes increased sixfold over control values by day 3, and then decreased 7 days after the injury. Maximal pressure within the bladder decreased in all spinal rats compared with controls. Smooth muscle cells were isolated from the urinary bladder, and their total protein and DNA content were measured by multiparametric cytofluorometry. DNA content of isolated smooth muscle cells decreased by day 3 and remained 7 days after the spinal injury. Total protein content of isolated smooth muscle cells was decreased 1 day after and increased 7 days after the spinal injury, just when spinal reflex of the bladder recovered. These findings suggest that hypertrophy of smooth muscle cells in urinary bladder is related to the activity of peripheral autonomic nerve and that smooth muscle cells already begin to hypertrophy during the spinal shock period to adjust themselves to the new state, that is, the spinal bladder.