In ME/CFS patients, we found that (1) the changes in the M-wave amplitude post-exercise, the alterations of the redox status induced by muscle exercise, and the CD26-expression level are correlated; (2) the LHS score was correlated to the alterations of the redox status induced by exercise and CD26-expression; (3) the pain component of MOS SF-36 was correlated to the CD26-expression level. Here, DPP4 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.