Patients with non-insulin-dependent diabetes mellitus frequently have been associated with elevation in plasma levels of PAI-1. Part of the variations in individual plasma PAI-1 levels have been attributed to variations in the PAI-1 gene. In order to determine whether insulin regulates PAI-1 expression in a genotype-specific manner, individual human umbilical vein ECs (HUVECs) were genotyped using a Hind III RFLP and incubated in the absence/presence of insulin. Treatment of 1/1 PAI-1 genotype HUVECs with insulin increased secretion of PAI-1 antigen approximately 1.7 to 2.2-fold and mRNA levels were increased approximately 1.8 to 2.8-fold. Treatment of HUVECs with actinomycin D or puromycin completely abolished the induction of PAI-1 by insulin. The nuclear run-on assays indicated approximately 3-4 fold increase in PAI-1 transcription rates. These in vitro studies with the 1/1 PAI-1 genotyped cultured HUVECs, suggests that hyperinsulinemia may be expected to increase EC PAI-1 synthesis in those patients with the responsive 1/1 genotype.