A single electroconvulsive shock in TO mice produced a drop in body temperature of 1.5–2°C, which was maintained for up to 60 min. This hypothermic response was not attenuated by the opioid antagonist i.p. naltrexone (0.3, 1 mg/kg); the α2-adrenoreceptor antagonist i.p. RX811059 (0.05, 0.5 mg/kg), or the benzodiazepine receptor antagonist i.p. Ro 15–1788 (10, 20 mg/ kg). The doses of antagonist used in this study had no effects on body temperature by themselves but significantly attenuated the hypothermia induced by their respective agonists, confirming their receptor-blocking activity. These findings suggest that electroconvulsive shock-induced hypothermia is not mediated by the release of either noradrenaline or by an endogenous ligand acting at opioid or benzodiazepine receptors.