Contrast sensitivity functions of foveal and of perifoveal upper and lower hemiretinal regions were measured in a population of twenty subjects. Foveal stimuli yielded consistently higher contrast sensitivities as well as a shift of the maximal sensitivity towards higher spatial frequencies as compared to perifoveal stimuli. The upper hemiretinal area was more sensitive at all spatial frequencies tested than the corresponding lower hemiretinal area. The statistical comparisons were highly significant, indicating not only regional retinal differences in visual acuity as reflected by the different contrast threshold levels at the highest spatial frequency, but also global differences between the upper and lower hemiretina systems not restricted to certain spatial frequency channels.