The effect of pilocarpine on the facility of aqueous outflow in normal human eyes was investigated up to 4 hours after the instillation of a 4% solution. The intraocular pressure, the size of the pupil, and the change in refractive state were also recorded. The present results indicate that the maximum increase in the facility of outflow occurs a half to one hour after the instillation of the drug, which coincides with that of the change in refractive state.