Autoradiography has demonstrated that a single injection of hydrocortisone (10mg/100 gm b.w.) reduced statistically significant the number of DNA synthesizing cells and the intensity of 3H-thymidine incorporation in these cells, as well as reduced the number of mitotically dividing epithelial cells in the rat ureter. 16 hours after hydrocortisone administration, the amount of proliferating cells increases statistically, but in 48 hours it reaches the control level.