Although there has been growing interest in general practitioners' participation in promoting health, little is known about the attitudes of their patients. Thus we sent a copy of a self administered questionnaire (the Health Survey Questionnaire) to 3452 patients aged 17-70 who were registered with two practices in north west London. Questions about attitudes to and perceptions of general practitioners' interest in weight, smoking, drinking, and fitness problems were included. The patients were also asked whether they thought that they had a problem in any of these areas. The response rate was 72%. Of those who responded, the proportions who thought that their general practitioners should be interested ranged from 72% in the case of fitness to 83% for weight, but only 38% thought that general practitioners had in fact been interested in fitness and only 48% thought so about weight. Forty one per cent of the respondents thought that they had a fitness problem, 42% a weight problem, and 59% of the smokers thought that they had a smoking problem. Four per cent of respondents stated that they had a drinking problem. Of those patients who said that they had a problem, the proportions who thought that their general practitioners had seemed interested ranged from 43% for fitness to 69% for smoking. The findings of this study suggest that greater participation by general practitioners in health promotion would be well received by most patients and that currently there may be considerable discrepancies between patients' expectations and their perception of their general practitioner's interest in these areas of preventive medicine.