Previous studies by the authors (1979) showed that a variety of noxious peripheral stimuli (mechanical, thermal, or visceral-chemical agents) induced a powerful inhibition of spinal dorsal horn convergent unit responses to transcutaneous electrical stimulation; the present study ascertained whether this inhibition—DNIC—is behaviorally significant and not merely an electrophysiological epiphenomenon. A behavioral paradigm was designed to determine whether painful visceral (electrical) stimulation could mask a complex, centrally integrated response to a punctual noxious stimulus and whether such inhibition could be reduced by moderate doses of naloxone. The algesic agent phenylbenzoquinone (PBQ) was used as the conditioning stimulus and a vocalization threshold test as the CS. Results indicate that a dull pain of visceral origin can block the behavioral response to punctual peripheral stimuli, thus supporting clinical observations in which pain patients show an increased experimental pain threshold. The hypoalgesia induced by visceral pain was dose-dependently antagonized by naloxone (0.2 mg/kg, iv), thus indicating the involvement of endogenous opiates. While naloxone depressed the vocalization threshold in PBQ-treated Ss, it had no significant effect in vehicle-treated controls, a finding that may be relevant to clinical reports on naloxone-hyperalgesia.(11 ref)(PsycINFO Database Record (c) 2016 APA, all rights reserved)