Data on the diagnostic accuracy of 3-MT are contrasting: even if same initial data suggested that the dosage of plasma 3-MT can increased the detection rate of pheochromocytomas and sympathetic PGLs, especially in SDHB and SDHD mutation carriers [16], a recent prospective study by Rao et al. [17] on 1963 screened subjects showed that 3-MT could increase false positive results. This evidence concerns the gene SDHD and pheochromocytoma.