To characterize the extent of activation of the hemostatic system and to detect local alterations which may favour thrombus formation we obtained samples from the right atrium (RA) and left ventricle (LV) of 60 stable angina patients (mean age 59 years, M/F: 49/11) during the cardiac catheterization procedure. None of the patients had a recent myocardial infarction or angioplasty. Plasma was prepared from citrated blood samples and the following parameters were determined: Thrombin-antithrombin (TAT) complexes, prothrombin fragment 1+2 (F1+2), plasmin-antiplasmin (PAP) complexes, tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor (PAI-1) activity and the levels of both u-PA activity (scu-PA) and antigen (u-PA Ag). Results were correlated with the angiographic findings. The analysis of the different parameters analyzed between patients with coronary stenosis or occlusion in one or more vessels (n=47) and without occlusion (n=13), showed no differences for TAT, PAP, F1+2, and PAI-1 activity between groups. However, a significant increase of t-PA antigen could be demonstrated in patients with occlusion (10.5±4.9 ng/ml) as compared to those with angiographically-verified coronary patency (7.5±3.2 ng/ml) (P<0.03), suggesting that t-PA may be a good marker for occlusion in these patients, u-PA results showed the lowest ratio in the more severe patients (59 vs 66%) (P<0.05). The scu-PA/u-PA ratio was also significantly reduced in the sample taken from RA as compared with LV (P<0.001). Our results point to an enhanced local activation of the fibrinolytic system in the more severe patients with stable angina pectoris and to atrioventricular differences in the u-PA components.