Elevated levels of PAI-1 are found in coronary artery disease (CAD) and non-insulin-dependent diabetes (NIDDM). PAI-1 may be involved in the pathogenesis of CAD through suppression of fibrinolysis, alternatively the high levels may result from vascular damage. There is evidence that PAI-1 levels are related to genotype at a PAI-1 promoter polymorphism. Genotype at this 4G/5G polymorphism was determined in 160 NIDDM (90 males and 70 females) patients with (n = 38) or without (n = 122) clinical evidence of CAD. Levels of cholesterol were higher (6.5 vs 5.9 mM, p < 0.01) and PAI-1 tended to be higher (PAI-1 activity 23.0 vs 20.4 U/ml) with CAD. The frequency of the 4G/4G genotype was increased and the 5G/5G genotype decreased, in the group CAD compared to those without (p < 0.05). These results suggest that possession of the 4G/4G PAI-1 promoter genotype is a risk factor for the development of CAD in subjects with NIDDM.