New thermally induced rearrangements in the furoxan series have been found: transformation of 3-(R)-substituted 4-(3-ethoxy-carbonylthioureido)-1,2,5-oxadiazole 2-oxides (furoxans) into derivatives of 5-amino-3-(α-nitroalkyl)-1,2,4-thiadiazole for R = Me, Ph, MeCO and into (5-amino-1,2,4-thiadiazol-3-yl)nitroformaldehyde arylhydrazones for R = N=N–Ar.