In cynomolgus monkeys, intracameral infusion of 0.2 to 5.0 mug of cytochalasin B caused an increase in outflow facility, as measured by two-level constant pressure perfusion. Cytochalasin B had its full effect in eyes which had undergone surgical disinsertion of the ciliary muscle from the scleral spur, and were therefore insensitive to pilocarpine. The cytochalasin effect was apparent in less than 20 min. and was largely reversible over a few hours. Thirty to 50 days after the infusion, facility was normal, and a second reaction could be elicited. No early or late damage to anterior segment structures was apparent by routine biomicroscopy during or after the single administration.