BACKGROUND Hypoxia is known to reduce performance. Adaptation is limited and requires special conditions. Heat and hypoxia have been shown to share some adaptive mechanisms. The purpose of this study was to test the possibility that prior heat acclimation may preserve performance under hypoxia. METHODS Eight young healthy men participated in this study. They went through two cognitive tests: Visual Vigilance Task (VVT) and Four Choice Reaction Time (FCRT); through a Dynamic Posture Test (DPT); and through an exercise onset of blood lactate accumulation rate (OBLA) test under moderate hypoxia (O2 = 15.6%) before and after 12 d of heat acclimation. RESULTS Maximal heart rate and core temperature were lower during the last day of heat acclimation compared to baseline (103 +/- 14 compared to 115 +/- 13 bpm and 37.59 +/- 0.20 compared to 37.83 +/- 0.28 degrees C, respectively). OBLA was higher after heat acclimation under both normoxic and hypoxic conditions. Blood oxygen saturation during walking at a pace of 7 km/h in hypoxic conditions was higher after heat acclimation compared to baseline (88 +/- 2% and 86.5 +/- 2%, respectively). Average steps during DPT in hypoxic conditions increased from 4.083 +/- 0.044 to 4.75 +/- 0.326 after heat acclimation. The VVT results under hypoxia did not change after heat acclimation, but false positive results were lower. The FCRT test results improved after heat acclimation (475 +/- 30 ms compared to 500 +/- 24 ms). CONCLUSIONS Prior heat acclimation may reduce physiological strain and improve cognitive performance in moderate hypoxia. Further studies are required in order to evaluate the possibility of implementing this method as an operational preconditioning tool.