1 The reduction in the sympathetic efferent discharge observed after propranolol may be due to either a central or a peripheral effect. The beta-adrenoceptor blocking drug, atenolol, is not thought to enter the brain and therefore any reduction in the level of sympathetic efferent discharge observed after atenolol is likely to be mediated peripherally rather than centrally. 2 Cats were anaesthetized with alpha-chloralose and artificially ventilated and a number of variables known to affect the sympathetic nerves were monitored throughout the experiment and maintained within normal limits. Recordings were made from few fibre preparations from the lumber trunk and the renal nerves. Blood pressure was either raised or lowered by the injection of phenylephrine (1-4 microgram/kg) or glyceryl trinitrate (2-20 microgram/kg) and the sympathetic efferent discharge was recorded over a range of blood pressures when the blood pressure was steady. 3 Thirty min after giving atenolol (3 mg/kg) the blood pressure, heart rate and sympathetic efferent discharge were significantly reduced. Atenolol also attenuated the reflex responses of the sympathetic nerves to changes in the blood pressure. 4 It is suggested tht atenolol has its actions on sympathetic nerves at a site outside the CNS and some possible mechanisms are discussed.