A steroid antagonist applied to one eye of 18 young pigmented rabbits during a 10-week period caused a statistically significant fall in IOP, but no statistically significant nor clinically relevant change in the rate of aqueous humor turnover. The pressure change is therefore ascribed to an alteration in outflow channels. No changes occurred in a parallel group of 5 animals in which one eye was treated with vehicle and the contralateral eye was untreated. The drug effects became evident after two weeks of application, suggesting that a slow turnover pathway is involved.