Ischaemic heart disease (IHD) risk factors, with particular reference to familial hypercholesterolaemia (FH), were studied in 39 male and 12 female Afrikaners aged 55 years or under in an intensive care unit immediately after an acute myocardial infarction and in the survivors at about 3 months after the infarct. Two major risk factors were found. Firstly, about three-quarters of both male and female patients smoked more than 15 cigarettes daily. Secondly, 51% of males and 37% of females had serum cholesterol values of greater than or equal to 7.0 mmol/l and about 20% of both men and women had levels of greater than or equal to 8.5 mmol/l. Three male and 2 female patients--1:10 of the whole sample--had FH diagnosed by rigorous criteria, a prevalence similar to the figure of 1:8 predicted from the frequency of FH heterozygotes in the Afrikaans-speaking population. None of the other IHD risk factors such as hypertension, diabetes and hyperuricaemia appeared to be important. The role of obesity appeared to be indirect by virtue of its frequent association with and possible contribution to hypercholesterolaemia. Many of the patients had a history of previous IHD episodes.