Some of the major lines of investigation that point to neurophysiological factors in spatial skill are presented. These lines include: the two hemispheres of the brain, recent studies, tachistoscopic studies, morphological differences between the cerebral hemispheres, Geschwind and Levitsky's discovery, cerebral dominance re-examined, sex differences in spatial ability, neuroanatomical basis for sex differences, a model for conceptualizing the effect of differential language lateralization on sex differences in spatial ability, and left-handedness and spatial ability. Further research is recommended. (CK)