Although SNX-ab was described as a highly potent and selective Hsp90α/β inhibitor (Ernst et al. 2014b), our in vitro autoradiography results indicated that binding of [11C]SNX-ab to both rodent brain and tumour (U87 and B16.F10 melanoma) tissue slices was not entirely Hsp90-specific, as blocking with relatively high concentrations of the authentic reference compound (SNX-ab), homologous inhibitor (SNX-0723) and heterologous pan-selective inhibitors (Onalespib, PU-H71) did result in only limited reduction of tracer binding. The gene discussed is HSP90AB1; the disease is melanoma.