The effect of two running sessions completedwithin a 12-h period on hemolysis, inflammation, and hepcidinactivity in endurance athletes was investigated. Tenmales completed two experimental trials in a randomized,counterbalanced order. The two trials included (a) a onerunning-session trial (T1) including 10 9 1 km intervalrepeats (90% peak _V O2 velocity), and (b) a two-runningsessiontrial (T2), comprising a continuous 10-km run (70%peak _V O2 velocity), and a 10 9 1 kminterval run (90% peak_VO2 velocity) completed 12 h later. Interleukin-6 (IL-6),free hemoglobin (Hb), haptoglobin (Hp), iron, ferritin, andhepcidin were assessed post-exercise. After the T1 and T2interval runs, free Hb was significantly increased and Hpsignificantly decreased (p B 0.05), with a cumulative effectshown in T2 after the second run (p B 0.05). The IL-6, serumiron, ferritin, and hepcidin activity were increased after eachrunning session (p B 0.05), with no cumulative effect in T2.In conclusion, a cumulative effect of two running sessions onhemolysis was shown, but no similar effect with inflammationand hepcidin activity was evident.