In the mouse tail-flick test, neither the racemate of N-allylnormetazocine (NANM) nor its optical isomers showed antinociceptive activity. However, all three antagonized morphine's tail-flick effects. In the phenylquinone test in mice, the racemate and (-)-isomer of NANM showed agonist activity and antagonized morphine-induced antinociception. The (+)-isomer was inactive. The opioid antagonist, naloxone was effective versus morphine alone in the tail-flick and versus morphine, and (+/-)- and (-)-NANM in the phenylquinone test. Yohimbine, the alpha 2-receptor blocker, antagonized morphine in the tail-flick test. In the phenylquinone test, yohimbine was effective versus (+/-)- and (-)-NANM, but showed no activity versus morphine. The results suggest that morphine and NANM are acting at different sites. In addition, different alpha 2-adrenoceptors appear to be involved. Some implications regarding the analgesic and psychotomimetic properties of NANM are discussed.