Genetic polymorphisms of apolipoprotein C-III (apo C-III) and insulin were studied in 48 Caucasian post-myocardial infarction patients. 10 patients (21%) had an uncommon allelic variant of the apo A-I/C-III gene cluster (on the long arm of chromosome 11); in 47 control subjects this variant was present in only 2 and in none of those who were normotriglyceridaemic. Distribution of genotypes between post-infarct and normotriglyceridaemic control groups was significantly different and the difference persisted when the normotriglyceridaemic subgroups of these patients were compared. In contrast, there was no difference in distribution of alleles at the highly polymorphic locus on the short arm of chromosome 11 adjacent to the insulin gene.