The cytochrome oxidase stain was applied to autopsy specimens of human brain. In primary visual cortex patches of darker enzyme staining were present in layers II, III, IVb, V, and VI. The patches were oval, about 400 by 250 <latex>$\mu m$</latex>, with a density of one patch per 0.6-0.8 mm<latex>$^2$</latex> of cortex. They were organized into rows spaced about 1 mm apart, intersecting the 17-18 border at right angles. The patches also stained preferentially for AChE activity. The lateral geniculate body was examined in two patients who died many years after losing one eye as adults. In atrophied laminae cytochrome oxidase activity was severely reduced. In the visual cortex from three cases after monocular enucleation, regular alternating light and dark columns of cytochrome oxidase activity were visible in layer IVc, presumably corresponding to ocular dominance columns. In two cases their pattern was reconstructed over 200-400 mm<latex>$^2$</latex> of striate cortex. The columns appeared as roughly parallel slabs about 1 mm wide, oriented perpendicular to the 17-18 border as in the macaque. In the upper layers light and dark rows of patches were present, which fit in register with the light and dark ocular dominance columns below. In layer IV the ocular dominance columns were also visible in Nissl stained sections as a consequence of secondary anterograde transneuronal degeneration. Darker Nissl stained columns matched lighter cytochrome oxidase stained columns corresponding to the missing eye. Quantitative measurements demonstrated a 10% loss of mean cell area and 35% increase in cell density in ocular dominance columns belonging to the missing eye, which accounts for their darker appearance in the Nissl stain. Patches were not present in a foetus at six months gestation. However, they were clearly formed in a six month old baby, although they appeared smaller and more closely spaced than in the adult. These results show that patches are present in man, in addition to other primates, although they appear proportionately larger. Ocular dominance columns are also present, in common with certain species of primates like the macaque, baboon and galago. Cytochrome oxidase histochemistry promises to be a useful technique for mapping anatomical features of the human brain post mortem.