Whether i.v. infusion of beta-endorphin or metenkephalin can modify adenosine-provoked angina pectoris-like pain was investigated in healthy volunteers with a double-blind controlled design. All seven volunteers experienced dose-related adenosine-provoked chest pain. Metenkephalin did not modulate the dose-effect curve for adenosine while beta-endorphin counteracted (p < 0.01) the development of pain. The results suggest that peripheral p.subtype opioid receptors are involved in the modulation and may play a role in the genesis of silent and painful myocardial ischaemia.