Argon blue-green laser and krypton red laser (KRL) photocoagulation were applied to primate retinas at intervals ranging from two to 23 days before the animals were killed. An injection of tritiated thymidine was given intravitreally three days before death. Argon blue-green laser photocoagulation induced cell proliferation in the retina and retinal pigment epithelium seven days after treatment, with quiescence at 23 days. Krypton red laser photocoagulation induced similar cell proliferation not only in the retina and retinal pigment epithelium but also around choroidal vessels and in the stroma of the choroid. Peak thymidine uptake occurred seven days after KRL treatment. There was less uptake at two and 11 days and no uptake at 23 days. Thymidine uptake in the retina and choroid also was detected with low levels of KRL treatment. True cell hyperplasia (cell division) occurred after laser treatment; only KRL treatment induced cellular reaction in the choroid.