Dexmedetomidine is a highly selective alpha 2-adrenoceptor agonist. In this study, the intrathecal administration of dexmedetomidine into the rat lumbar subarachnoid space produced dose-dependent, prolonged antinociception as measured by hot plate and tail flick testing. Intrathecal administration of 3 or 10 micrograms of dexmedetomidine increased hot plate and tail flick latencies to cutoff values within 15 min of injection. Animals receiving 1 microgram of intrathecal dexmedetomidine did not show any significant antinociception when compared to saline controls. The intrathecal administration of the alpha 2-adrenoceptor antagonist, idazoxan, ablated all measurable antinociception produced by the prior injection of 10 micrograms of dexmedetomidine.