The ability of sufentanil to suppress noxiously evoked activity of wide dynamic range (WDR) neurons was studied in decerebrate, spinal-cord-transected cats. Sufentanil, 2.5 ug (n = 7) or 5.0 ug (n = 7), when administered spinally, produced a significant, dose-dependent suppression of noxiously evoked (51 °C radiant heat stimulus) activity of WDR neurons in the dorsal horn of the spinal cord. Spontaneous recovery from sufentanil suppression was not seen for up to 2 h. Reversal following intravenous naloxone, 0.12 mg, although present, was not as complete as that seen following other spinal opiates. Intravenous sufentanil, 5.0 ug/kg (n=4), produced significant but short-lasting depression of noxiously evoked WDR neuron activity. A comparison of the results of this study with data from a previous fentanyl study suggests that sufentanil may be more appropriate than fentanyl for spinal or epidural administration because of a possible longer duration of action. However, the lesser degree of naloxone reversal seen in this study may suggest that, clinically, reversal of sufentanil effects may be more difficult.