The mass spectra of several diaryltriazenes (I), 1,2,3-benzotriazin-4(3H)-ones (II), 1,2,3-benzotriazines (III)—(V), and anhydro-bases of benzotriazinium salts (VI) were compared and contrasted. The mass spectra show abundant evidence for complex rearrangement during fragmentation, and in some cases there are similarities to both photolytic and thermolytic reactions of these compounds.