Vinyl radicals have been prepared by the methyl-radical sensitised decompositions of acraldehyde and vinyl formate; attempts to obtain the radicals directly by photolyses of acraldehyde and divinylmercury were unsuccessful. Ratios of rate constants (?) for like- and cross-disproportionation to like-and cross-combination, determined at 175°, are: ?(Vinyl, Vinyl)= 1-1, ?(Me, Vinyl)=2-3.