This human plasminogen activator inhibitor type 1 (PAI-1) total antigen assay is intended for the quantitative determination of total PAI-1 in human plasma. The assay measures PAI-1 antigen in the 0.25-100 ng/ml range. Samples giving PAI-1 levels above 100ng/ml should be diluted in blocking buffer or plasma devoid of PAI-1 before use. The concentration level of PAI-1 antigen in pooled normal human plasma ranged from 7.4-28 ng/ml.