This study determined the influence of nor-binaltorphimine (nor-BNI, 10 micrograms intracisternally), 1, 7 and 21 days post-administration, upon spiradoline-induced antinociception measured in the hot-plate test. On each test day, nor-BNI prevented the spiradoline-induced increase in the latency of rats to paw-lick without affecting the antinociceptive response to morphine. These data suggest that a single administration of nor-BNI can cause a long term blockade of kappa-opioid receptors in rats.