General practitioners in one health district were surveyed by postal questionnaire (including 15 sample electrocardiogram tracings) to assess their usage and competence in interpretation of the electrocardiogram. A response rate of 60% was achieved, of whom 40% said they used the electrocardiogram at least monthly and 43% used it 'always' or 'usually' in patients with suspected myocardial infarction at home. Overall competence in recognizing a variety of abnormalities was felt to be good. Recent qualification, the possession of a higher qualification (MRCP/MRCGP) and frequency of usage were associated with better performance. Even so, unequivocal acute myocardial infarction was misdiagnosed by 20% of respondents. These findings have implications for the provision of electrocardiographic services in primary care and the management of patients in the home with suspected myocardial infarction, particularly with the advent of thrombolytic therapy.