These studies were performed to investigate a role of PAF in the genesis of life-threatening arrhythmias and platelet aggregation accompanying myocardial ischaemia and reperfusion. Pretreatment with the PAF antagonists SRI 63-441 (10 mgkg-1 iv) and BN 52021 (5 mgkg-1 iv) significantly reduced the number of arrhythmias during a thirty minute coronary artery occlusion period in open-chest anaesthetised greyhounds, particularly ventricular tachycardia. Both drugs also reduce the incidence of ventricular fibrillation resulting from reperfusion of the myocardium. Myocardial ischaemia in control animals resulted in a marked fall in platelet count in blood draining the ischaemic area, which was abolished by both SRI 63-441 and BN 52021. These results suggest a role for PAF in the genesis of ischaemia and reperfusion-induced arrhythmias, possibly by inducing platelet aggregation.