Abstract The superior colliculus of the human brain was studied in autopsy material stained by the acetylthiocholinesterase methods of Geneser-Jensen & blackstad (1971) and Karnovsky & roots (1964) . The histochemical findings suggest that in the human, as in common laboratory mammals, the superior colliculus is characterized by a periodic vertical segmentation in addition to a horizontal stratification into layers. In frontal sections through the superior colliculus in each of three human brains, acetylthiocholinesterase staining in the middle gray layer was distributed in a series of 200–400 μm wide patches separated by less densely stained zones. The patches were irregular in shape and some were composed of a core of intense enzyme activity surrounded by a rim of weaker stain. Comparable concentrations of the enzyme were not apparent in the superficial collicular layers. Dorsalview reconstructions of the enzyme patches were prepared in two cases from drawings of serial sections. The resulting planar maps showed that the patches present in frontal sections form parts of narrow bands of varying length that run in a roughly longitudinal direction through the colliculus. This pattern of banding is remarkably similar to that observed with cholinesterase methods in the intermediate gray layer of the cat superior colliculus and recalls also the bands formed by nigrotectal terminals in this layer. It is not yet clear which tissue elements are being stained by the cholinesterase method. Nevertheless, the finding of histochemically distinct repeating units in the human superior colliculus demonstrates the existence, in the brain of man, of a periodic ordering with many of the characteristics of columnar organization.