Some (25-50%) dorsal column postsynaptic (DCPS) neurons respond only to innocuous mechanical stimuli; the remainder (50-75%) responds to both innocuous and noxious mechanical stimuli. Those that respond to noxious mechanical stimuli (pinch) are assumed to be excited by input from nociceptive primary afferents, but it is conceivable that their pinch-evoked responses are produced by the inadvertent activation of those low-threshold mechanoreceptive primary afferents that respond to stretching the skin. Because nociceptive primary afferents respond reliably to noxious heat and low-threshold mechanoreceptors do not, we tested DCPS neurons in the cat lumbar spinal cord with a series of noxious heat stimuli (48 degrees C or 50 degrees C-56 degrees C; 30 s duration). Seven of eight pinch-responsive neurons responded to noxious heat, but only after their receptive fields had been sensitized by prolonged or repeated heating. The results show that (1) many DCPS neurons in the cat are excited by nociceptive primary afferents and (2) these nociceptive afferents are probably myelinated high-threshold mechanoreceptors.