Throughout Europe, including Norway, increased winter mortality from cardiovascular diseases (CVD) is well described. However, while there are associations between high CVD mortality and cold climate, the reason for the excess deaths is not entirely known. Recent epidemiological evidence suggests that brief outdoor exposure to cold conditions may be linked to increased winter mortality in the elderly. However, the question as to whether alterations in the haemostatic system following exposure to cold could be responsible for the increased winter risk has been little investigated in elderly subjects. In this study, we have compared the effect of exposing lightly clothed healthy elderly men and women (60-70 years) for 90 minutes to either a mild cold stress (16 degrees C) or thermoneutral conditions (28 degrees C). Measurements of a variety of autonomic and haematological parameters were made in order to compare to what extent exposure to cold stress affects production of thrombogenic risk factors. The overall autonomic responses clearly showed that the subjects were mildly cold exposed. The main changes in the blood system were a cold exposure increase in hemoconcentration and an increase in the fibrinolytic parameter, t-PA. This coupled with other changes support previous findings and it is concluded that short term mild cold exposure in the elderly initiates a mild inflammatory reaction and a tendency for an increased state of hypercoagulability.