A voice region has recently been identified in the monkey auditory cortex which prefers species-specific vocalizations and is sensitive to the vocal differences among monkey callers. To better understand the sensitivity of this and other brain regions for species-specific vocalizations, we independently manipulated two components in monkey vocal sounds. After recording the coo vocalizations from 4 rhesus monkeys, we either shifted the position of the fundamental frequency (which is established by the vocal source in the larynx) or shaped the dispersion of the higher, formant frequencies (established by the acoustical filtering that occurs in the vocal tract above the larynx). The manipulations left the sounds within the species-typical range. We then used high-resolution functional imaging (fMRI) to evaluate the sensitivity of the rhesus monkey brain to independent changes of the two vocal components. Initial results revealed that many regions along the auditory-cortical processing hierarchy were sensitive to changes in both the fundamental and formant frequencies. In the earlier stages of cortical processing, especially in the caudal auditory regions, the sensitivity of the auditory fields to changes in the fundamental and formant frequencies depended upon each fields topography of preferred sound frequency (tonotopy), which we mapped separately. For example, the sensitivity of the auditory field A1 to manipulation of the fundamental frequency