We studied a new fluorophotometric method to determine trabecular outflow facility in man. Pilocarpine was selected to evaluate this non-invasive method, since its primary ocular hypotensive effect is to increase trabecular outflow facility. Levobunolol was used to decrease intraocular pressure and aqueous humor flow required for the calculation of trabecular outflow facility. In ten ocular hypertensive patients trabecular outflow facility in the pilocarpine-treated eyes was 0.42 +/- 0.16 (S.D.) microliters min-1 mmHg-1 compared with 0.17 +/- 0.14 microliters min-1 mmHg-1 in the vehicle-treated eyes (P less than 0.004). An ocular hypotensive additivity was also found in the eyes treated with both drugs. It was concluded that this non-invasive fluorophotometric method may be useful in evaluating the effect of a drug on trabecular outflow facility.