Cyclodialysis was performed in one eye of each of eight cynomolgus monkeys. Two days later, the intraocular pressure was 1.6 +/- 0.7 mmHg in eyes with cyclodialysis and 12.0 +/- 0.7 mmHg in fellow control eyes. 10(-4) M fluorescein-isothiocyanate dextran (70,000 molecular weight) was perfused into the anterior chamber of each eye for 30 min. The eyes were enucleated and dissected into sclera, choroid, retina, iris, and ocular fluid. Samples were homogenized and centrifuged, and the fluorescence of the supernatant was measured. Expressed as equivalent volumes of aqueous, the rate of anterior chamber movement of tracer via uveoscleral pathways was 1.40 +/- 0.17 microliter/min in cyclodialysis eyes and 0.34 +/- 0.10 microliter/min in control eyes. Cyclodialysis results in a fourfold increase in uveoscleral outflow, contributing to the observed hypotony.