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The purposes of this study were to assess Vo2max and submaximal endurance time to exhaustion (ET) during acute cold-air exposure. Eight male subjects ( age = 19.9 yr) were alternately exposed in groups of four to chamber temperatures of +20°C and −20°C for 30 h each. A week was allowed between exposures. Maximum oxygen uptake was measured using a mechanically-braked cycle ergometer, and ET was determined on the same ergometer using a 17-min/3-min exercise/rest schedule until the subject was unable to maintain pedal rate. Maximum oxygen uptake was not significantly different between conditions: 3.43 ± 0.09 l.min−1 at +20°C and 3.35 ± 0.10 1.min−1 at +20°C. During endurance exercise, intensities equaled 77.1 ± 1.4% and 78.9 ± 2.0% of Vo2max at + 20°C and −20°C, respectively. Heart rate and Vo2max values obtained between 8 and 10 min of the endurance run were not significantly different (156 ± 2 bpm and 2.63 ± 0.08 l.min−1 at + 20°C and 158 ± 3 bpm and 2.65 ± 0.11 l.min−1 at −20°C). Endurance time to exhaustion however, decreased 38% (P<0,05) from 111.9 ± 22.8 min at +20°C to 66.9 ± 13.6 min at −20°C. The data support the contention that aerobic capacity is not altered by cold exposure but suggest a marked decrease in submaximal endurance performance.