THE sensation of a single sound event can be altered by subsequent sounds. This study searched for neural mechanisms of such retroactive effects in macaque auditory cortex by comparing neural responses to single tones with responses to two consecutive tones. Retroactive influences were found to affect late parts of the response to a tone, which comprised 53/134 of the recordings of action potentials and 88/131 of the recordings of field potentials performed in primary, caudal, and medial auditory fields. If before or during the occurrence of the late response to the first tone a second tone was presented the late response was suppressed. Suppression of late cortical responses parallels perceptual phenomena like backward recognition masking, suggesting that suppression of late responses provides a neural correlate of auditory backward effects.