The study investigated TRPM3 ion channel function in people with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) in a large, multi-center sample. TRPM3 activity was measured electrophysiologically (whole-cell patch-clamp recordings) in natural killer (NK) cells in 36 healthy subjects and ME/CFS patients who met Canadian diagnostic criteria. TRPM3-like currents between groups were statistically compared and the influence of different laboratory sites was also evaluated. The results showed a significant reduction of TRPM3 function in NK cells of ME/CFS patients compared to controls in all analyzed parameters. At the same time, no significant influence of different laboratory locations on the measurement results was demonstrated. The study thus confirmed previous findings about TRPM3 dysfunction in NK cells in ME/CFS. The authors report that these results support the involvement of TRPM3 in the pathogenesis of ME/CFS and strengthen the evidence that TRPM3 may be a potential biomarker for the diagnosis of this disease.