Cynomolgus monkeys underwent unilateral panretinal scatter photocoagulation (PRP) and/or nasal and temporal horizontal retinal meridional photocoagulation (HRMP) with xenon arc or argon or krypton laser light. Shortly thereafter, in the PRP-treated eyes, accommodative responsiveness to topical eserine and electrical stimulation of the Edinger-Westphal nucleus (EWN) was diminished, accommodative responsiveness to intramuscular (i.m.) pilocarpine was enhanced, and the number of muscarinic receptors in the ciliary muscle was reduced compared to the contralateral controls. In most instances, these parameters returned to normal over 6-12 wks and the abnormalities could be induced again by another round of PRP. However, in some PRP-treated eyes, accommodative responsiveness to EWN stimulation and topical eserine remained subnormal permanently (greater than 1 yr). Shortly after HRMP alone, accommodative responses to i.m. pilocarpine, topical eserine, and central stimulation did not differ markedly in the treated and control eyes. Morphologic studies 1 to 78 wk following PRP revealed that myelinated and unmyelinated nerves within the entire circumference of the choroid and ciliary muscle were severely damaged early on. The number of unmyelinated nerves between the individual ciliary muscle fibers was drastically reduced, those which remained were swollen or deteriorated, and agranular synaptic vesicles were rarely seen. Thereafter, the nerves in the choroid and ciliary muscle gradually regenerated. Following HRMP, only the choroidal nerves which passed through the photocoagulated areas and the ciliary muscle nerves in the corresponding meridians showed signs of deterioration, and there was minimal effect on the physiologic responses examined. These findings collectively indicate that intraocular parasympathetic denervation of the ciliary muscle is produced by PRP, although all nerve types are likely damaged.