During physiological stress, plasma is shifted to the extravascular space resulting in a concentration of diffusible blood constituents. This haemoconcentration is important to most haemostasis factors because they are too large to pass through endothelial pores with plasma. Research has established that blood is hyper-coagulable after exercise in normoxia, as seen by a shortening of activated partial thromboplastin time (aPTT). However results for prothrombin time (PT) & thrombin time (TT) remain equivocal. In hypoxia, studies have shown both activation & suppression of coagulation. Reasons for these differences have been attributed to the use of varying protocols & study populations. Both hypoxia & exercise independently contract plasma volume (PV), yet interpretive implications of this remain unexplored. The purpose of the present study was to evaluate & compare the independent effects of hypoxia & exercise on coagulation times with & without correction of PV. 18 healthy males were recruited & administered 6 hours passive exposure to normobaric hypoxia (Fraction of inspired oxygen [FIO2] 12%). After exposure, they performed an incremental cycling test to exhaustion. Blood was sampled at three time points: FIO2 21% [Normoxia rest], after 6 hours exposure [Hypoxia rest] & post hypoxic exercise [Hypoxia exercise]. It was then tested for plasma levels of Fibrinogen (FB), PT, TT & aPTT. Comparing all results to normoxia rest, in uncorrected data (PV-) there were no significant differences in any marker at hypoxia rest. However, FB was significantly increased and aPTT significantly shortened at hypoxia exercise. PT and TT remained unchanged. Upon correction for PV (PV+) the changes in FB and aPTT were abrogated & there were significant elongations of PT & TT at hypoxia exercise. FB & aPTT remained unchanged. These data suggest blood coagulation is affected by PV. The question of whether or not to correct for plasma volume remains a clinically important concept that deserves consideration.