Previous studies suggested that krypton laser photocoagulation was more effective in the treatment of macular diseases than argon laser. Furthermore, it could perform photocoagulation more effectively in some lesions with subretinal hemorrhage, because the krypton laser beam was poorly absorbed by hemoglobin. In the present experiment, hemorrhagic retinal detachment was produced in monkey eyes with Q-switched Nd-YAG laser, and 4 weeks later photocoagulation was performed with krypton and argon lasers to compare the differences in the effects of these two lasers. When the subretinal hemorrhage and a heavy coagulation effect was produced in the detached retina, but no coagulation effects were observed in the choroid. Krypton laser beam could go through the hemorrhage and certain coagulation effects were observed in the choroid and the detached retina. It is suggested that krypton laser photocoagulation is more effective in the lesions behind subretinal hemorrhages than photocoagulation with argon laser.