Comparisons were made between the effects of binocular suture and dark rearing in terms of: (1) the state of visual cortical physiology after prolonged deprivation; and (2) the nature of physiological recovery seen when monocular vision was experienced after prolonged deprivation. These comparisons were based on the ocular dominance distribution and receptive field tuning characteristics of visual cortical cells. After prolonged dark rearing, most visual cortical cells were binocularly activated and had non-specific receptive field properties. Monocular vision after dark rearing produced dramatic changes: the majority of cells were responsive only to the open eye and these cells typically displayed orientation and direction selectivity. Prolonged binocular suture, on the other hand, resulted in a high incidence of unresponsive cells and cells with unmappable receptive fields, and a low proportion of binocularly responsive cells. Monocular vision experienced after binocular suture resulted in only slight physiological changes, and there was no evidence for selective development of connections from the open eye. These results indicate that dark rearing and binocular suture have different effects on the development of cat visual cortical cells. Diffuse visual stimulation through the sutured lids (binocular suture) appears to produce permanent developmental effects on cortical physiology, whereas complete deprivation (dark rearing) leaves cortex in a state which can be modified by subsequent visual experience.