Leuchter's opposition to the possibility of homicidal gassings at Auschwitz relies on residual cyanide remains found in the homicidal gas chambers and delousing chambers at Auschwitz. While both facilities were exposed to the same substance (Zyklon B), many of the delousing chambers are stained with an iron based compound known as Prussian blue, which is not apparent in the homicidal gas chambers. It is not only this disparity that Leuchter cites, but accordingly from his samples (which included measurements of it) that he claims he measured much more cyanide in the delousing chambers than in the gas chambers, which he argues is inconsistent between the amounts necessary to kill human beings and lice. This argument is often cited by Holocaust deniers, and similar claims are also made by Germar Rudolf.