The objective of this study was to determine the effect of acute moderate hypoxia and rest duration on performance and on the accumulated oxygen deficit (AOD) in high-intensity intermittent efforts. After preliminary tests, 2 groups of nonacclimatized men (resident at 690 m above sea level) carried out 3 randomized protocols of effort (EXP1, EXP2, and EXP5) on 3 different days. These tests were performed at acute moderate altitude (2,320 m) by the hypoxia group (H) and in normoxia by the normoxia group (N). During EXP1 the subjects ran a maximum of five 400-m sprints (90% intensity) on a treadmill, with a pause between efforts of 1 minute. In EXP2 and EXP5 the same protocol was repeated, increasing the rest period between sprints to 2 and 5 minutes, respectively. Lactate accumulation and exhaled gases were measured during the tests. Accumulated oxygen deficit was calculated for each sprint. The total AOD (SigmaAOD) for each type of protocol was determined to be the sum of the corresponding accumulated deficits. The AODs were influenced by the length of rest period (p < 0.05) but not by H. The increase in recovery time between sprints increased the SigmaAOD (7,843 +/- 4,435 vs. 7,137 +/- 2,117 ml; 11,013 +/- 4,616 vs. 9,931 +/- 2,731 ml; 12,611 +/- 4,594 vs. 12,907 +/- 3,085 ml for H and N in EXP1, EXP2, and EXP5, respectively). The AOD increased in value when the same sprint was compared from EXP1 to EXP5 (p < 0.05). The results obtained show that exposure to acute moderate altitude does not affect the anaerobic pathway contribution in intermittent high-intensity exercises. Performance during this type of repeated effort is not altered during acute exposure to moderate altitude, which should be taken into account when an acclimatizing period is not possible.