In line with our hypothesis of a role of vasoactive AAB in ME/CFS, we found that levels of alpha1/2- and beta1/2/3-AdR-, M3/4-AChR-, and AT1-R-, ETA/B-R-AAB/IgG ratios all significantly correlate with the severity of fatigue and, with the exception of beta3-AdR-AAB/IgG, with muscle pain. This evidence concerns the gene AGTR1 and myalgic encephalomeyelitis/chronic fatigue syndrome.