The auditory regions in four normal brains were mapped and the full extent of the cytoarchitectonic subdivisions was measured for the presence of right-left asymmetries. It was found that asymmetries similar to those found in the planum temporale (left commonly larger than right) are also seen in auditory cytoarchitectonic area Tpt, and area of probable importance for language function. There is a strong positive correlation between the planum asymmetry and the asymmetry of Tpt. It is concluded that the previously described planum asymmetries probably reflect asymmetries in an auditory cytoarchitectonic area and therefore may represent, at least in part, the anatomic substrate for language lateralization.