Thermolysis of N-benzoyl-N′-phenylthiourea (BPTU) on heating in air at 230°C gives NH3, H2S, benzaldehyde, benzil, aniline, azobenzene, benzamide, benzanilide, phenylisothiocyanate, phenyl-cyanamide, thiocarbanilide and benzoylisothiocyanate, whereas thermolysis of N-benzoy1-N′-benzylthiourea (BBTU) affords NH3, H2S, benzaldehyde, benzil, toluene, bibenzyl, stilbene, benzamide, cyanamide, benzylisothiocyanate, benzoylthiourea and benzoylisothiocyanate. Thermolysis of N-benzoyl-N′-α-naphthylthiourea (BNTU) under the same conditions gives NH3, H2S. benzaldehyde, benzil, benzamide, α-naphthylisothiocyanate, α-naphthanilide, α-naphthylcyanamide. benzoylisothiocyanate, α-naphthylamine and N,N′-di-α,α′-naphthylthiourea. Analogous results were also obtained on photolysis of (BFTU), (BBTU) and (BNTU) with the exception of NH3, and the photodegradation products of phenylthiourea, benzylthiourea and a-naphthylthiourea respectively. The main feature of these pyrolyses is the homolysis of the amide and thioamide bonds providing free radicals that undergo different reactions involving H-abstraction, dimerization, coupling, fragmentation, rearrangement and disproportionation to yield the identified products.