Pearlman¿s catalyst is commonly used in various hydrogenation, arylation and O-debenzyaltion reactions. The catalyst is unusual that it is active but not pyrophoric. It is commonly written as palladium (II) hydroxide supported on carbon, Pd(OH)2/C. However, we have recently shown that hydrous palladium oxide consists of a poorly crystalline core of PdO ~18 Å in diameter capped with a monolayer of hydroxyls and all covered with several layers of water. Thus it is a core-shell structure rather than stoichiometric Pd(OH)2 as previously suggested. In view of this result, here must be a strong suspicion that the commonly accepted formulation of Pearlman¿s catalyst is not the reality. INS spectroscopy on TOSCA can readily distinguish between hydroxides and water so will provide unequivocal characterisation of the nature of the active material in Pearlman¿s catalyst.