The authors investigated the relationship of plasma insulin to some risk factors of ischaemic heart disease (IHD). They examined 79 healthy men--drivers of international truck transport with a normal glucose tolerance. The group comprised 21 men with hyperinsulinaemia. This group was compared with 21 men from the same group with normal insulin levels. The two groups were comparable (matched pairs) for age, occupation, cigarette and alcohol consumption and education. Significantly higher values of the body mass index (BMI), systolic and diastolic blood pressure were found in the group with hyperinsulinaemia. The latter group had a significantly more frequent positive family-history as regards cardiovascular diseases. After 48 months all subjects were checked. Two men from the entire group had died (43 and 48 years) from fatal myocardial infarction, both had hyperinsulinaemia. Manifestations of cardiovascular diseases (IHD and hypertension) developed in 12 subjects from the group with hyperinsulinaemia, as compared with two subjects with hypertension but normal insulin levels. To conclude, it may be stated that healthy subjects with hyperinsulinaemia and a normal glucose tolerance have a higher level of some risk factors of coronary heart disease (hypertension, obesity, positive family-history), as compared with the normoinsulinaemic group, and a poorer prognosis as regards cardiovascular morbidity and mortality.