The impact of long-term, heavy exercise on recently established cardiovascular/thromboembolic risk factors of the fibrinolytic system, tissue plasminogen activator (tPA) and plasminogen activator inhibitor (PAI-1) in relation to food composition was studied. Twenty healthy men, aged 18-55 years participated in a 14-day skiing tour through the Swedish mountains, carrying a pack load of 30 kg, and spending each night in self-dug igloos (ambient temp -10 degrees to -25 degrees C), and were randomized to 2 food regimens having 30 or 40 energy percent of fat. Individual records were kept of all consumed food. Citrated plasma was obtained before and after 1 and 2 weeks of exercise: tPA release was assessed by a 10 min venous occlusion (VO) test. At baseline, daily dietary fiber intake correlated negatively with PAI-1 activity. Already after the first week of the skiing tour there were significant drops in PAI-1 activities, cholesterol and triglycerides. The tPA mass concentrations also dropped, both before and after VO, but tPA activities were unchanged, as were von Willebrand factor (vWF) levels. These changes were related mainly to the expenditure of energy, calculated from the food consumption, and appeared to be mediated through changed insulin sensitivity and decreased body fat mass. The energy percent of fat in the food had no differential impact. The effects receded a few weeks after cessation of the endurance exercise. Thus, endurance physical activity improves the fibrinolytic risk factor profile by reducing PAI-1 while leaving tPA activity unaffected, independently of food composition. A low dietary fiber intake appears to be associated with higher PAI-1 activities at baseline.