In the present study, we used whole-cell patch-clamp technique as a method to measure endogenous TRPM3 activity in IL-2 stimulated NK cells from HC and ME/CFS patients, enabling the ion channel current recordings under voltage-clamp conditions and observation of the shape of the TRPM3 current–voltage relationship (I–V). Here, TRPM3 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.