1. Partial outflow obstruction induces marked changes in detrusor contractile function and morphology. One common finding in all experimental animal models of partial outflow obstruction is a significant increase in bladder mass. 2. Previous studies have demonstrated that partial outlet obstruction induces a rapid and substantial increase in [3H]thymidine incorporation into virtually all cellular elements of the bladder. 3. The present study was designed to investigate the [3H]thymidine uptake and localization induced by exposure of the in vitro whole rat bladder model to various intravesical pressures and rates of intravesical infusion. 4. The results are as follows: (a) There were no differences in DNA concentration between control and other groups. (b) Slow infusion induced a mild increase in DNA synthesis ([3H]thymidine incorporation) at 0.5 ml and a significantly greater level of DNA synthesis at 1.6 ml. (c) [3H]thymidine incorporation was significantly increased by exposure to 7.5 cm H2O, 15 cm H2O, and 30 cm H2O. (d) Exposure to 60 cm H2O and 90 cm H2O did not initiate an increase in [3H]thymidine incorporation. (e) Autoradiography showed that all tissue elements (urothelium, connective tissue, smooth muscle) participated in the response.