A significant reduction in cold-induced vasodilation (CIVD) is observed at high altitudes. No agreement is found in the literature about acclimatization effects on CIVD. Two studies were performed to investigate the effect of altitude acclimatization on CIVD. In the first study 13 male subjects immersed the distal phalanx of the left middle finger in water of 0 degrees C for 30 min to evoke CIVD. Five subjects were exposed to altitudes of 5,100 to 7,000 m for 45 days (A). Eight subjects were exposed to an altitude of 5,100 m for <3 days (NA). The groups did not differ in age, weight, and stature. No significant differences were observed between A and NA. However, the maximum finger skin temperature of group A tended to return to sea level values (6.9 +/- 3.2 degrees C at sea level vs. 6.0 +/- 0.7 degrees C at altitude), while a strong reduction was observed for the NA group (7.7 +/- 4.3 degrees C vs. 3.7 +/- 3.1 degrees C). This indicates that the CIVD response at altitude tended to be stronger for the acclimatized subjects. In a second study, nine males were followed in a longitudinal study. CIVD was measured before, during and after 7 days of exposure to 4,350 m. Maximum finger skin temperature before and after exposure did not differ (8.5 +/- 2.6 degrees C vs. 7.8 +/- 1.6 degrees C), and was reduced at altitude. There was no difference in maximum finger skin temperature between the 7 days at altitude (e.g., 5.3 +/- 2.7 degrees C at day 2 and 4.7 +/- 1.1 degrees C at Day 7). It can be concluded that no acclimatization effects of CIVD occur during the first 7 days of altitude exposure, but that differences may occur after altitude exposure of several weeks.