SUMMARY1. The cardiovascular effects of isoprenaline and propranolol injected through a cannula chronically implanted into a lateral cerebral ventricle were examined in unanaesthetized dogs.2. Intraventricular isoprenaline (50–200 μg) produced tachycardia and the highest dose consistently produced a fall in blood pressure. No pressor response occurred in these doses.3. Intraventricular propranolol (600 μg–2 mg) produced variable cardiovascular responses. Consistent abolition of the cardiovascular responses to intraventricular isoprenaline occurred only with a dose of 2 mg propranolol, but this dose also abolished the responses to intravenously injected isoprenaline (1–2 μg/kg).4. Pretreatment with hexamethonium (10 mg/kg, intravenously) and guanethidine (5 mg/kg, subcutaneously daily for 3 days) potentiated the cardiovascular responses to intraventricular isoprenaline. Pretreatment with atropine methonitrate (0.4 mg/kg, intravenously) reduced the depressor response to intraventricular isoprenaline but did not convert the response into a pressor one.5. The results in the unanaesthetized dog are at variance with those reported in the unanaesthetized cat in which intraventricular isoprenaline produces a pressor response, and therefore do not support the general proposition that central β‐adrenoreceptor activation leads to an elevation of blo