Over the past 40 years in England and Wales the rise in mortality from coronary heart disease has continued unabated among working-class men, whereas among professional men the rate has changed little for the past 20 years. As a result it is now 26 per cent higher in social class V compared with social class I. The difference in women is larger (+ 152%), and it has been present for at least 40 years. The social class gradient for men was confirmed in a survey of 17530 London civil servants aged between 40 and 64 (the Whitehall Study). When men in the lowest employment grade were compared with those in the top (administrative) grade, the age-adjusted prevalence rate was 53 per cent higher for angina, 77 per cent higher for ischaemic-type electrocardiographic abnormalities, and 75 per cent higher for the prevalence of electrocardiographic abnormality among men with angina. At follow-up, the seven-and-a-half year coronary mortality was 3.6 times higher in the lowest than in the top grade. This social class difference was partly explained by known coronary risk factors: men in the lower grades smoked more and exercised less, they were shorter and more overweight, and they had higher blood pressures and lower levels of glucose tolerance. Most of the difference, however, remains unexplained. It seems that there are major risk factors yet to be identified, and that these may throw light on how it is possible for members of a highly-placed social group to have a relatively low risk of coronary heart disease.