1 Transmural stimulation of intrinsic sympathetic nerves and exogenous catecholamines produce /I-adrenoceptor mediated relaxant responses in strips of contracted sheep coronary artery.2 The neuronal uptake inhibitors, metaraminol, cocaine and desipramine and the extraneuronal uptake inhibitor, cortisol, failed to potentiate responses to noradrenaline or sympathetic stimulation; responses to isoprenaline were enhanced by cortisol. 3 Oxytetracycline, which inhibits binding to connective tissue fibres, did not affect responses to noradrenaline or nerve stimulation. 4 17,B-Oestradiol, caffeine and U0521 proved to be unsuitable compounds for studying catecholamine inactivation since they non-selectively potentiated responses to noradrenaline and isoprenaline. 5 It is concluded that catecholamine inactivation processes do not modify transmitter function in sheep coronary arteries.