Suprathreshold fundus lesions produced by ruby and argon laser photocoagulation were studied within 24 hours by light and electron microscopy. It was shown that damage was maximal in the outer retina in all ruby laser lesions and extramacular argon laser lesions. In both monkey and human, inner retinal damage occurred independently of outer retinal damage in macular lesions produced by the argon laser. In lesions produced by equal energy, inner retinal damage was more severe in humans than in monkeys. In both species outer retinal damage was less severe in the foveal than the parafoveal region and this disparity was greater in humans than in monkeys. These findings are important to the therapeutic use of argon laser energy for mascular disease. In particular, absortion of energy in the inner retina reduces the energy available in the treatment of subretinal lesions in the foveal area, and causes unwanted neuroretinal damage. The higher sensitivity to argon laser irradiation of the human fovea compared with the monkey fovea, has not been appreciated when defining laser safety limits.