The aim was to examine the relationships between serum ferritin and risk factors for ischaemic heart disease (physical activity, body mass index, tobacco smoking, alcohol consumption, serum total cholesterol, serum triglycerides, serum high-density lipoprotein (HDL) cholesterol, systolic and diastolic blood pressures). Epidemiological population survey performed at the Copenhagen County Centre for Prevention of Disease in 1982-84. The participants were selected at random from the census register and comprised 2235 healthy Caucasian Danes, all non-blood-donors (1044 men and 1191 women), in cohorts of 30, 40, 50 and 60 years of age. The participants gave a detailed medical history and had a clinical examination including blood samples. In both men and women, all risk factors displayed a significant increase with age. In men aged 40-60 years, significant positive associations were found between serum ferritin and the following risk factors: body mass index, alcohol intake, serum triglycerides, and systolic and diastolic blood pressures. There was a significant negative association between serum ferritin and tobacco smoking. There was no association between serum ferritin and physical activity, serum total cholesterol or serum HDL cholesterol. In women aged 40-60 years, significant positive associations were found between serum ferritin and the following risk factors: body mass index, alcohol intake and serum triglycerides. There was no association between serum ferritin and physical activity, tobacco smoking, serum total cholesterol, serum HDL cholesterol or blood pressure. Associations were found between serum ferritin and some risk factors for ischaemic heart disease in men and women. The clinical significance of these findings remains to be clarified. One may hypothesize that the 'missing link' between serum ferritin and ischaemic heart disease in men is the relationship between serum ferritin, serum triglycerides and blood pressure.