Mayvat brilliant red AF has been identified as a halogenated derivative of 3: 4: 9: 10- dibenzopyrene-5: 8-quinone (II), the latter being obtained by dehalogenation of Mayvat brilliant red AF or Indanthrene scarlet 4G with Raney nickel, aqueous sodium hydroxide and hydrogen. Reduction of (II) with aluminium tricyclohexoxide gave 3: 4: 9: 10-dibenzopyrene (I), a potent carcinogen, which was isolated by Bonnet and Neukomm from tobacco smoke ...