Haemorheological variables (whole-blood, plasma and relative blood viscosity, haematocrit, red cell aggregation, white cell count and fibrinogen) were measured in 753 men and 821 women aged 25-74 years, and related to cardiovascular risk factors and prevalent cardiovascular disease (CVD). Men had higher levels than women of blood viscosity, haematocrit, corrected viscosity and relative viscosity. Post-menopausal women had higher levels than pre-menopausal women of blood viscosity, haematocrit, corrected blood viscosity, plasma viscosity and fibrinogen: each of these differences was completely or partly abolished by use of hormone replacement therapy. Serum total cholesterol, triglycerides, diastolic blood pressure, body mass index and smoking markers showed positive associations with most rheological variables, whereas HDL-cholesterol, plasma vitamin C and social class showed inverse associations. Rheological variables were associated with prevalent CVD after age-adjustment. However, after multiple risk factor adjustment only plasma viscosity and red cell aggregation showed significant (P<0.04) associations in both men and women (comparing top to bottom quarters). Plasma interleukin-6 (measured in a 25% subsample of 196 men and 221 women) correlated significantly with age, fibrinogen, white cell count, plasma and blood viscosity, current smoking, and (in men) with low serum vitamin C levels; but not with other major risk factors or with prevalent cardiovascular disease.