Twenty-two cynomolgus monkeys underwent unilateral total iridectomy in vivo. Several weeks to several months postoperatively, intraocular pressure (IOP) was determined bilaterally by manometry under pentobarbital anesthesia (15 monkeys), by a minified Goldmann applanation tonometer under CI-744 anesthesia (16 monkeys), and by a minified Draeger applanation tonometer under light phencyclidine catalepsia (4 monkeys). Mean IOP in aniridic eyes was about 0.3 mm Hg, or about 3%, lower than in opposite eyes. IOPs of aniridic and opposite eyes of the individual monkeys were highly correlated in all groups. In 11 monkeys, resting total outflow facility and the facility response to intravenous pilocarpine were determined 6 to 9 weeks postoperatively by two-level constant-pressure perfusion under pentobarbital anesthesia. There were no significant differences between mean resting facility, postpilocarpine facility, or facility response to pilocarpine of aniridic and opposite eyes. Resting facility, postpilocarpine facility, and facility response to pilocarpine in aniridic and opposite eyes of the individual monkeys were each highly correlated. Total iridectomy in the cynomolgus monkey apparently has little, if any, effect on IOP, outflow facility, or facility response to intravenous pilocarpine, and the iris plays little, if any, role in mediating the facility response to intravenous pilocarpine.