Several parameters of aqueous humor dynamics were measured in 11 human subjects before and after exposure of one eye to a continuous stream of cold air. In the treated eye, I.O.P. was found to decrease significantly from a mean +/- SD pre-treatment value of 14.1 +/- 2.3 mmHg to a post-treatment value of 12.6 +/- 2.6 mmHg. Episcleral venous pressure was found to decrease significantly from a pre-treatment value of 6.2 +/- 1.3 mm Hg. No significant changes were found in aqueous flow or total outflow facility, indicating that cold air exposure decreased I.O.P. by causing a decrease in episcleral venous pressure.