Exercise induced variations in coagulation and fibrinolytic activities were evaluated in 25 endurance horses competing in a 80 km ride. Venous blood samples were collected before exercise, after 40 km and 30 min after 80 km. Haematological parameters, fibrinogen, clotting times (aPTT and PT) and the main inhibitors (AT-III and α2-antiplasmin) activities were determined. Furthermore, we assessed thrombin-antithrombin complexes (TAT) as a marker of coagulation activity; and fibrinogen degradation products (FgDP) and fibrin degradation products D-dimers (FbDP) as markers of fibrinolytic activity using immunoenzymatic tests. Significant changes in all haemostatic parameters were found after endurance exercise. A significant (P < 0.001) increase of TAT values was found when comparing pre-race (mean ± s.d. 2.28 ± 0.9), at 40 km (3.45 ± 1.2) and 30 min after 80 km (4.0 ± 1.9 ng/ml). Values of FgDP before, at 40 km and after 80 km showed a significant (P < 0.0001) decrease (mean ± s.d. 445.0 ± 144.4, 210.0 ± 111.1 and 177.7 ± 77.2 ng/ml) and the values of FbDP showed a slight but significant (P < 0.001) increase (mean ± s.d. 875.4 ± 230.9, 1062.0 ± 310.0 and 737.2 ± 305.3 ng/ml). These changes confirm a hypercoagulable state, a marked hypofibrinogenolysis and a slight hyperfibrinolysis during endurance exercise. No significant differences were found between the results from horses that finished (n / 19) and those eliminated because of fatigue (n = 6).