BACKGROUND Persistent microalbuminuria in diabetic patients is a risk factor of cardiovascular mortality. Increased plasma plasminogen activator inhibitor type-1 (PAI-1) levels have been observed in diabetic patients with overt nephropathy. However, there have been few studies on diabetic patients with microalbuminuria. The expression of PAI-1 may be influenced by the polymorphism of the PAI-1 genotype promoter. The aim of this study was to investigate the relationship between the plasma PAI-1/t-PA levels, polymorphism of the PAI-1 4G/5G promoter and microalbuminuria in type 2 diabetes. METHODS: The plasma PAI-1/t-PA levels and polymorphisms of the PAI-1 promoter were measured in type 2 diabetic patients without nephropathy (n=30), and with microalbuminuria (n=30) and overt proteinuria (n=20). The correlation between the amount of urinary albumin excretion and plasma PAI-1/t-PA levels were investigated using Pearson's correlation analyses. RESULTS: The plasma PAI-1/t-PA levels and polymorphisms of the PAI-1 promoter showed no significant difference between the three groups in relation to the urinary albumin excretion. There were no differences in the plasma PAI-1/t-PA levels between the genotypes of the polymorphism of the PAI-1 promoter. No association was found between the amount of urinary albumin excretion and the plasma PAI-1/t-PA levels and genotypes of the polymorphism of the PAI-1 promoter. CONCLUSION: These results show that there was no decrease in the fibrinolytic state in type 2 diabetics with microalbuminuria, compared to normoalbuminuria, which also suggest that polymorphisms of the PAI-1 4G/5G promoter do not affect the plasma PAI-1/t-PA levels in type 2 diabetic patients with microalbuminuria.