1. dl-Propranolol, l-propranolol, dl-alprenolol, pindolol (LB46), practolol, ICI 66082, sotalol and oxprenolol all produced prolonged falls in blood pressure and heart rate after intracerebroventricular administration in conscious normotensive cats.
2. Transient initial pressor responses and tachycardias were observed after intracerebroventricular infusions of all the β-adrenoceptor antagonists used, except ICI 66082.
3. d-Propranolol, d-alprenolol, procaine and lignocaine all produced initial increases in blood pressure and heart rate but did not subsequently cause any reduction in either blood pressure or heart rate.
4. The time of maximum hypotension and bradycardia after intracerebroventricular infusion of β-adrenoceptor antagonists coincided with the maximum inhibition of the centrally mediated tachycardia observed after intracerebroventricular isoprenaline.