The effects of early visual experience and later unilateral neocortical lesions on the behavior of male hooded rats were measured on an open-field, 17-arm spatial maze, and a visual field or perimetry test. The comparison of behavior observed in the open field revealed that light-reared (LR) rats that suffered a right hemispheric lesion were more active and reared more than any of their dark-reared (DR) counterparts as well as LR animals that had left hemispheric or sham operations. On the radial maze task in which 8 of 17 arms were baited, the rats with unilateral lesions performed less effectively than did the sham-operated animals. The effect of the lesions was significantly greater for LR rats than their DR counterparts. The perimetry testing revealed that although the operated animals did react to stimuli throughout their visual field, some contralateral neglect was evident in the case of both LR and DR rats. The lesions did have a much greater impact on orientational behavior of operated LR rats. However, as was the case with respect to performance on the radial maze, no evidence emerged of any functional asymmetry following the unilateral cortical lesions. The results are discussed in terms of Denenberg's (1981) hypothesis about cerebral and functional asymmetry in the rat.