There are considerable differences in the central processing of somatic and visceral pain and little is known about the role of the rostral ventromedial medulla (RVM) in descending modulation of visceral hyperalgesic states. In the present experiments we have investigated the responses of RVM “on” and “off” cells to a visceral noxious stimulus – intracolonic (IC) instillation of capsaicin (CAP) – and compared them with the responses to intradermal (ID) injection of CAP in their somatic receptive fields. Extracellular recordings were made from RVM neurons in anaesthetized Sprague Dawley male rats. RVM “on” and “off” cells were identified by their responses to noxious pinch of the tail and to a noxious heat ramp applied to the right hindpaw. CAP (0.1 %, 200 μl) or saline (SAL, 200 μl) was instilled into the colon and neuronal activity was followed for at least 1 hour. In others animals, CAP (0.1%, 30 μl) or SAL (30 μl) was injected ID into the left hindpaw. IC CAP increased the firing of on-cells from baseline 0.91±0.43 to a maximum of 5.52±1.32 spikes/s; a response that lasted more than 45 minutes and decreased slowly. Off-cells firing baseline was 7.62±0.76 and IC CAP did not modify this activity. ID CAP had little effect on either cell type. No changes in firing rate were observed with IC or ID SAL injections. These results show that a visceral noxious stimulus elicits a strong and sustained response in RVM on-cells which may contribute to the sustained central hyperexcitability induced by visceral noxious events.