Scotland has one of the highest mortality rates from coronary heart disease for both men and women. However within Scotland there are major geographical differences in the mortality rates, exemplified by the differences between the two largest Scottish cities. Glasgow on the west has a much higher mortality rate for cardiovascular diseases than Edinburgh in the east. During 1986 coronary risk factor population surveys were conducted simultaneously in Edinburgh and North Glasgow as part of the WHO MONICA study. These surveys employed standardized methods and the central quality control of the WHO project. Measures of coronary heart disease morbidity were higher in North Glasgow, except for electrocardiographic evidence of ischaemia, consistent with the mortality rates. The major coronary risk factors were uniformly higher in North Glasgow than in Edinburgh, except for serum lipids which were not significantly different. The risk factors, except the lipids, showed a gradient by socioeconomic status, so that when the risk factors levels were standardized for housing tenure the significant differences between the cities largely disappeared, and the serum cholesterol levels in women become significantly higher in Edinburgh because of their slight negative relationship with social status. This study shows that the socioeconomic differences between Edinburgh and North Glasgow largely explain the coronary risk factor differences between the cities. The socioeconomic differences in coronary disease and its major risk factors require further investigation and may be more fundamentally important than the geographical differences in the patterns of coronary heart disease.