In the first Whitehall study, plasma cholesterol was a strong predictor of coronary heart disease (CHD) but it showed a positive association with grade of employment: the higher the grade the higher the level. Because it could not explain the higher rate of CHD in lower employment grades, further investigation of biochemical CHD risk factors has been conducted with data from the baseline examination of the Whitehall II cohort in 1985-88. These data also allow investigation of gender differences and the effect of menopause. Serum cholesterol (6860 men and 3374 women) and apolipoproteins A-I and B (apo AI and apo B) were measured in those aged 35-55 working in the London offices of twenty Civil Service departments. Plasma fibrinogen and factor VII were determined in 45-55 year olds. The apo B/apo AI ratio (95% confidence interval) after age adjustment is lowest in premenopausal women: 0.557 (0.549-0.565), intermediate in postmenopausal women: 0.601 (0.589-0.613) and highest in men: 0.703 (0.698-0.709). After age adjustment fibrinogen is higher in postmenopausal (2.90 (2.85-2.95) g/l) than in premenopausal women (2.78 (2.71-2.84) g/l), who have higher levels than men (2.64 (2.62-2.67) g/l). A positive association with employment grade is seen for apo AI and a negative association is seen for fibrinogen, apo B (women only) and the apo B/apo AI ratio, after age adjustment. These patterns are consistent with the higher rates of CHD in lower grades. Cholesterol and factor VII show no gradient with our sensitive measure of social position. After adjusting for the effects of smoking rates, alcohol consumption, exercise and dietary pattern, as well as age, ethnicity, body mass index and report of symptoms, the regression coefficient for apo AI on employment grade is reduced by 43% in men and 70% in women. Corresponding reductions for fibrinogen are 53% and 65%. These attenuations suggest that a considerable part of the social gradients in apo AI and fibrinogen are explained by variations in health related behaviours. The remaining gradients may represent effects independent of these behaviours.