Several groups have shown that fibrinolytic capacity is impaired in survivors of myocardial infarction, due to increased levels of the fast-acting plasminogen activator inhibitor (PAI). In order to study the behaviour of PAI in patients with coronary heart disease, 180 patients with angina pectoris were investigated. They were 148 males and 32 females, ages ranging from 29 to 70 years (52.8 ± 8.2, mean ± S.D.). A sex- and age- matched normal population served as a control (n=105, age-range 30 to 69 years, 52.4 ± 7.9). PAI was determined by a functional titration assay, and its activity expressed as arbitrary units (AU). PAI levels were significantly (p <0.005) higher in patients with angina (24.3 ± 10.3 AU/ml, range 10.1 to 112.0 AU/ml) than in normals (20.4 ± 4.6 AU/ml, range 10.5 to 31.6 AU/ml). PAI levels were unrelated to sex or age, in both the patient and the control groups. As expected, plasma triglyceride levels were correlated to PAI in patients (r=0.19, p<0.01) and in normals (r=0.20, p<0.05). Patients with a history of previous myocardial infarction (n=114) had similar PAI levels as patients without infarction (24.2 ± 11.1 AU/ml as compared to 24.4 ± 9.6 AU/ml). It is concluded that PAI levels are elevated in patients with coronary heart disease, whether myocardial infarction has taken place or not.