Abstract The ambident nucleophilic behaviour of some 2-amino-5-H-1, 3, 4-thiadiazoles in alkylation, acylation and nitrosation reaction has been verified. The structures assigned to the 2-amino-1, 3, 4-thiadiazoles (1a-i) and to the Δ 2-1, 3, 4-thiadiazolines (2a-e) agree with the spectral data.