This study investigated 1) red blood cells (RBC) rigidity and 2) lactate influxes into RBCs in endurance trained athletes with and without exercise-induced hypoxemia (EIH). Nine EIH and six non-EIH subjects performed a submaximal steady-state exercise on cyclo-ergometer at 60% of maximal aerobic power for 10 min followed by 15 min at 85% of maximal aerobic power. At rest and at the end of exercise, arterialized blood was sampled for analysis of arterialized pressure in oxygen (PaO₂), and venous blood was drawn for analysis of plasma lactate concentrations and hemorheological parameters. Lactate influxes into RBCs were measured at three labelled [U-¹⁴C] lactate concentrations (1.6, 8.1 and 41 mM) on venous blood sampled at rest. The EIH subjects had higher maximal oxygen uptake than non-EIH (p<0.05). Total lactate influx was significantly higher in RBCs from EIH as compared to non-EIH subjects at 8.1 mM (1498.1 ± 87.8 nmoles.ml^-1.min^-1 vs. 1035.9 ± 114.8 nmoles.ml^-1.min^-1; p<0.05) and 41 mM (2562.0 ± 145.0 nmoles.ml^-1.min^-1 vs. 1618.1 ± 149.4 nmoles.ml^-1.min^-1; p<0.01). MCT-1-mediated lactate influx was also higher in EIH at 8.1 mM (p<0.05) and 41 mM (p<0.01). The drop in PaO₂ was negatively correlated with total lactate influx measured at 8.1 mM (r = -0.82, P < 0.05) and 41 mM (r = -0.84, P < 0.05) in the two groups together. Plasma lactate concentrations and hemorheological data were similar in the two groups at rest and at the end of exercise. The results showed higher MCT-1-mediated lactate influx in the EIH subjects and suggested that EIH could modify lactate influx into erythrocyte. However, higher lactate influx in EIH subjects was not accompanied by an increase in red blood cell rigidity.