OBJECTIVE--To assess, in the context of their possible role in prehospital thrombolysis, the ability of general practitioners to recognise acute transmural myocardial ischaemia/infarction on an electrocardiogram. DESIGN--150 doctors (every fifth name) were selected from the alphabetical list of 750 on Merseyside general practitioner register and without prior warning were asked to interpret a series of six 12 lead electrocardiograms. Three of these showed acute transmural ischaemia/infarction, one was normal, and two showed non-acute abnormalities. Details of doctors' ages, postgraduate training, and clinical practice were sought. SETTING--General practitioners' surgeries and postgraduate centres within the Merseyside area. PARTICIPANTS--106 general practitioners (mean age 45 years) agreed to participate. MAIN OUTCOME MEASURE--Accuracy of general practitioners' interpretations of the six electrocardiograms. RESULTS--82% of general practitioners correctly recognised a normal electrocardiogram. Recognition of acute abnormalities was less reliable. Between 33% and 61% correctly identified acute transmural ischaemia/infarction depending on the specific trace presented. Accurate localisation of the site of the infarct was achieved only by between 8% and 30% of participants, while between 22% and 25% correctly interpreted non-acute abnormalities. Neither routine use of electrocardiography nor postgraduate hospital experience in general medicine was associated with significantly greater expertise. CONCLUSION--The current level of proficiency of a sample of general practitioners in the Merseyside area in recognising acute transmural ischaemia/infarction on an electrocardiogram suggests that refresher training is needed if general practitioners are to give prehospital thrombolysis.