Receptive field properties of cells in the dorsal lateral geniculate nucleus (LGNd) were examined in 3 groups of rabbits, each subjected to monocular visual deprivation by lid suture at differing age periods. Monocular deprivation occurring from 6--8 to 20--25 days of age affected the normal development of LGNd receptive fields. A significant proportion of the cells in the deprived LGNd were either unresponsive to visual stimulation or had vague, indefinite receptive fields. Significantly fewer cells with uniform fields were found in the deprived LGNd than in the control. Percentages of concentric, motion and directional cells did not differ between the deprived and control LGNd. The diameters of receptive fields for concentric cells with sustained response properties, however, were smaller in the deprived than in the control LGNd. When deprivation was continued to 87--121 days of age, the percentage of uniform, indefinite and non-responsive cells found in the deprived LGNd approached more normal levels. Percentages of concentric, motion and directional cells were also normal. Monocular deprivation commencing at 21--22 days of age also had disruptive effects on LGNd receptive field organization, as reflected in the lower percentage of uniform and increased percentages of indefinite and non-responsive cells. These deficits, however, were not as severe as those seen in the animals deprived at an early age. A fourth group of adult rabbits subjected to monocular lid suture showed no such detrimental deficits in receptive field organization. These results demonstrated that visual deprivation affects the predominantly monocular LGNd of the rabbit, and that a critical period exists for such effects.