Absolute thresholds for pure tones, loudness, frequency and intensity difference thresholds and the resonance of the external auditory meatus were measured in chimpanzees and compared with those in humans. Chimpanzees were more sensitive than humans to frequencies higher than 8 kHz but less sensitive to frequencies lower than 250 Hz and 2- to 4-kHz tones. Difference thresholds for frequency and intensity were greater in chimpanzees than in humans. The resonance of the external ear was about the same in the two species. The effects of differences in hearing between species upon speech perception are discussed.