1 The effects on blood glucose of four substances with analgesic properties (apomorphine, pethidine, codeine and etorphine) and of prostaglandin E(1) were examined in unanaesthetized cats. They were applied by the intraventricular route being either injected into a lateral ventricle or infused into the fourth ventricle through implanted Collison cannulae.2 Apomorphine gave rise to pronounced hyperglycaemia in a dose of 0.75 mg which produced scarcely any hyperglycaemia on intravenous injection. It was more effective on infusion into the fourth ventricle than on injection into a lateral ventricle and was approximately half as potent as morphine in provoking hyperglycaemia.3 Codeine produced no hyperglycaemia in doses of 0.75 and 1.5 mg.4 Pethidine had a weak hyperglycaemic action in doses of 0.75 and 1.5 mg, but the effect was not regularly obtained. Potency of the drug was at most only a third to a sixth that of morphine.5 Etorphine produced strong hyperglycaemia on infusion into the fourth ventricle in a dose of 10 mug. Unlike apomorphine or morphine it was more potent on injection into a lateral ventricle when it produced a strong hyperglycaemic response in doses of 5 or 1 mug, which were subthreshold on infusion into the fourth ventricle. However, this response may have been brought about indirectly as a result of severe asphyxia and of convulsions associated with the injections. On infusion into the fourth ventricle, etorphine was about 75 times as potent as morphine in producing hyperglycaemia.6 Prostaglandin E(1) had no hyperglycaemic action when infused into the fourth ventricle in a dose of 400 ng.