Abstract: The electron impact and field desorption mass spectra of 10 2,4-diamino-6-substituted quinazoline sulfonamides were investigated. In some of the EI and FD spectra, rearrangement and elimination of SO2 were observed. By means of accurate mass measurements and metastable ion determination the fragmentation pattern is described, and the conditions of the formation of M-SO₂⁺ rearrangement ion are discussed.