Monkeys and human subjects were exposed to a series of thermal stimuli before and after a 53 degrees C, 30-second burn to the glabrous skin of the hand. The responses of C- and A-fiber nociceptive afferents in the monkeys and subjective responses by the humans were compared. The burn resulted in increased sensitivity of the A fibers, decreased sensitivity of the C fibers, and increased pain sensibility (hyperalgesia) in the human subjects.