A new specific ski ergometer has been developed to study aerobic endurance and force development in the upper body of cross-country skiers. The major purpose of the present study was to examine the validity and the reliability of this ergometer. Eleven male cross-country skiers participated in the study. Work on the ski ergometer, at an inclination of 4 degree, incorporated the double-poling technique. All subjects participated in three tests in addition to a pretest where peak oxygen uptake in the upper body (VO2peak) and maximal oxygen uptake during treadmill running (VO2max) were measured. In a field-test, subjects performed double poling uphill, and VO2peak was reached after 4-6 min. There was no statistically significant differences in power output (Watt) or oxygen uptake (VO2) at the same exercise stages between tests and the coefficient of variation was 2.0% and 2.5%, respectively. There were no significant differences between VO2peak as measured in the field and on the ski ergometer. The average upper body/leg ratio was 90% (range 78.1-97.1%). There was no significant correlation between VO2max and VO2peak. The present study showed the ski ergometer to be both reliable and valid for evaluating VO2 and force development in the upper body at submaximal and maximal workloads for cross-country skiers.