As we showed here, unactivated ex vivo lymphocytes are quiescent and dying, so that a difference between patient and control groups in the depth of this quiescence and/or the rate of cell death can explain the previously reported reduction in mitochondrial activities in ME/CFS lymphocytes. We found that ME/CFS lymphocytes die at a dramatically faster rate in culture medium than control lymphocytes. It is likely that in previous studies, the ME/CFS lymphocytes assayed for mitochondrial activity included a higher proportion of dead cells than did the controls.