Decompositions of N-nitrosoacetanilide, m- and p-t-butyl-, m-, p-, and o-chloro-N-nitrosoacetanilides in benzene, and other solvents, in the presence of arynophiles such as anthracene and its derivatives, 2,3,4,5-tetra-arylcyclo-pentadienones, and 1,3-diphenylisobenzofuran gave, with the exception of the last named nitrosamide, aryne adducts corresponding to the anilide used, in yields varying from 4 to 82%. None of these nitrosamides gave the corresponding aryne adduct with furan at 15°. p-t-Butyl-N-nitrosoacetanilide in the presence of tetraphenylcyclopentadienone gave 6-t-butyl-1,2,3,4-tetraphenylnaphthalene, rather than the isomeric 1-(p-t-butyl-phenyl)-2,3,4-triphenylnaphthalene, thus indicating the intermediary of a bidentate rather than a monodentate species. Competition experiments in which pairs of arynophiles were allowed to compete (a) for authentic benzyne (b) for the intermediate produced by N-nitrosoacetanilide gave almost identical results in both cases, indicating that benzyne is involved in case (b) also. A mechanism involving removal of a proton ortho- to the diazonium function in the intermediate benzenediazonium acetate is proposed and an explanation for the anomalous behaviour of furan is advanced in terms of a fast competing radical chain reaction of the latter.