The mass spectra of ions in flame ionization detector (f.i.d.) type flames containing iron and lead compounds show that, in addition to metal ions, prominent species of formula (MoxHx+1)+ are present which are apparently protonated metal hydroxides. For FeOH2+ and PbOH2+, however, the structure of these species may be identical with those of metal-ion hydrates. This work confirms the presence of Pb+ ions in flames to which lead compounds are added, but, in general, metal or metal-containing ions should not affect the saturation current obtainable in an f.i.d, used to detect organometallic compounds. Ionization of iron and lead and their oxides and hydroxides by H3O+ may contribute to atmospheric ionization in the presence of metallic pollutants.