Growing evidence supports the concept that neutrophils accumulating in reperfused ischaemic myocardium play a detrimental role in evolving infarction. Lignocaine, an antiarrhythmic drug commonly used clinically, interferes with neutrophil function in vitro and potentially in vivo. To test the hypothesis that lignocaine may influence infarct size by reducing neutrophil accumulation in reperfused ischaemic myocardium, 31 dogs underwent a 2 h occlusion of the left anterior descending coronary artery, followed by 6 h of reperfusion. One group of dogs received saline (controls) the other a perfusion of lignocaine 0.06 mg.kg-1.min-1 starting 30 min before coronary occlusion and lasting for the duration of the experiment. Blood lignocaine concentrations at the onset of reperfusion were 3.3(0.6) micrograms.ml-1. 111Indium labelled autologous neutrophils were injected at the time of occlusion and their accumulation in the myocardium measured by digital scintigraphy of heart slices. The area at risk and infarct size were evaluated by planimetry of the heart slices (7 mm) after perfusion of Evans blue dye and triphenyltetrazolium staining. Ventricular fibrillation occurred in six controls and in five dogs receiving lignocaine. The phenomenon occurred early during the occlusion period in the lignocaine group (five dogs) and at reperfusion in controls (five dogs; p less than 0.05). In the remaining 20 dogs, 10 in each group, a linear correlation was found between myocardial 111In labelled neutrophil and circulating neutrophil counts at the onset of reperfusion (r = 0.076, p less than 0.05) and with infarct size (r = 0.96 and 0.74, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)