A series of experiments addressed the issue of comparability among neurological processes in pigmented rat and human visual systems. In the first set of experiments, transient visual-evoked potentials (VEPs) were elicited by the onset of sine-wave gratings of various spatial frequencies. The spatial frequency-response profiles of the first positive and immediately succeeding negative components differed from one another, but were similar in the two species. In addition, amplitude of the negative, but not the positive, component was strongly attenuated in both species following stationary pattern adaptation. In the second set of experiments, steady-state VEPs were elicited by the onset and offset of the gratings. The spatial frequency profiles of the 1F (response amplitude at the frequency of stimulus onset-offset) and 2F response components differed from one another, but were similar in both species. The final set of experiments indicated that diazepam, a GABA agonist, reduced amplitude of 2F, but not 1F, in both species. These results suggested that at least some functional subsystems mediating spatial vision in humans may have qualitatively similar counterparts in rats.