THE precipitated abstinence syndrome consists of a series of behavioural events which appear in morphine-dependent organisms after the administration of narcotic antagonists. Martin1 has suggested that some precipitated abstinence signs arise because an error force is generated when a narcotic antagonist resensitises a homeostat previously altered by a narcotic. Recently, in studies on the neuroanatomical correlates of morphine withdrawal, we found that brain areas associated with the wet shake behaviour of precipitated abstinence in the rat seemed to be closely adjacent to central pathways of heat dissipation and heat gain2-4. As morphine has complex effects on central thermoregulatory mechanisms5, the possibility was considered that the generation of an error signal in central thermoregulatory systems may account for the appearance of some precipitated abstinence signs. To test this hypothesis, we investigated the effects of environmental temperature on the precipitated abstinence syndrome.