Laboratory of Neurophysiology, University of Wisconsin, Madison, Wisconsin, USA The distribution of best frequencies of neurons and neuron clusters was mapped on the superior temporal plane of the macaque monkey. Primary auditory cortex (A1) comprises a complete and orderly cochlear representation. It is coextensive with a cytoarchitectonic field often referred to as koniocortex. Cochlear apex (low frequency) is represented rostrolaterally within the field and cochlear base (high frequency) caudomedially. A small region of the cochlear partition is found represented in a band of auditory cortex; that is neurons with very similar best frequencies are arrayed both vertically and horizontally. Surrounding A1 4 other fields are found that on both anatomical and physiological grounds stand apart from the primary field. In two of them the data suggest the way in which they are topographically organized. In addition there appear to be auditory areas extending further rostrally on the plane and onto the lateral surface of the superior temporal gyrus.