In the intermediate gray layer of the superior colliculus there is a lattice of high NADPH-diaphorase activity which represents the terminal distribution of a number of extrinsic afferent systems. These include inputs from the dorsal cholinergic column and cells in the precommissural nucleus and dorsolateral wedge of the central gray substance. Other afferents that terminate in the intermediate gray layer, such as the input from the nucleus of the brachium of the inferior colliculus (BIN), are almost completely segregated from the above inputs and show very little overlap with the NADPH-diaphorase lattice. It is suggested that the input from the precommissural nucleus and central gray substance may have a role in nociception while the input from BIN may provide an important source of auditory information.