The apparent in vivo dissociation constant (1<A) and relative efficacy values for alfentanil, Etonitazene, morphine, and nal-buphine were determined by comparing the effects of these agonists in the presence of buprenorphine with the effects of these agonists alone in the rhesus monkey tail-withdrawal pro-cedure. Initial time course studies of buprenorphine alone mdi-cated that 3.2 and 10 mg/kg produced increases in tail-with-drawal latencies when studied with 48#{176}Cwater for 48 hr.

More still,: No increases in tail-withdrawal latency were found with either dose studied with 55#{176}Cwater. Buprenorphine produced dose-de-pendent shifts to the right for the antinociceptive effects of alfentanil, Etonitazene, morphine and nalbuphine 72 hr after administration and decreased the maximal effects of morphine in 48#{176}Cwater and those of alfentanil and Etonitazene in 55#{176}C water. Buprenorphine administration decreased the receptor