The substrate-specificity of a newly described enzyme common to six bacterial species, comprising five different genera, isolated from such widely divergent sources as decomposing fish, well-water and surface taint butter, was investigated. Of the various substrates studied only trialkylamine oxides having the general structure R3 ≡≡ N = 0 were activated with subsequent reduction, the corresponding volatile base being formed in each case. Betaine, choline, acetylcholine, ergothioneine and stachydrine containing an atomic group similar to the above were not activated. The designation "triamineoxidease" is proposed for this enzyme.