Schaefferals were identified as chromogens responsible for the development of an orange to red color after treating the caps of certain Agaricus species with aniline and nitric acid (Schaeffer's cross reaction). The structures of schaefferals A and B were confirmed by total synthesis. The color reaction can be explained by reaction of their aldehyde group with aniline and protonation of the azomethine thus formed, yielding a red delocalized cation.