The electrolytic brain lesion technique was used to assess the role of the nucleus amygdaloideus centra]is in the mediation of the catalepsy and stereotyped bchaviom" induced in the rat by the narcotic agonists and antagonists. M6029 and M6007 exhibif~d a biphasic action in the rat consisting initially of catalepsy induction followed by the development of stereotyped gnawing, biting and licking responses with a transition period when both behaviours were appareat. Morphine and M320 produced a cataleptic response in the rat but stereotyped bchaviour did not develop. Bilateral ablation of the nucleus amygdaloideus centralis was found to abolish the cataleptic phase of the effects of M6029 and M6007 and to markedly enhance the stereotypie phase. The lesions were similarly shown to markedly reduce or abolish the cataleptic effects of morphine and M320 and, in contrast to the actions of these drugs in normal animals, a periodic stereotyped behaviour developed. A role is suggested for the nucleus amygdaloideus contrails in the genesis of the cataleptic action of the narcotic agonists and antagonists. An amygdaloid-cataleptic: striatal-stereotypic balance is hypothesised for the action of these agents in the rat.