A novel synthesis is described in which potassium t-butoxide dehalogenation of beta,beta-dihaloalkyl sulphides is used to prepare unsaturated episulphides and limitations of the method are discussed. For example, 31 undergoes monodehydrochlorination to 32, while 50 and 51 fail to react. The intermediacy of sulphonium ions is supported by the conversion of isomeric dihalides, 35 and 40, to the same episulphide, viz 44.