The syntheses of a number of conjugates of 1,1'-thiobis(2-chloroethane) ("sulphur mustard") and its simple derivatives with cysteine, N-acetylcysteine and N-acetylcysteine methyl ester are described. These compounds were synthesised for use as reference compounds to support metabolite identification in metabolic studies and, in some cases, to provide standards for analytical procedures being developed for the retrospective confirmation of exposure to sulphur mustard.