The arylmercuric arenesulphinates, PhHg(SO2Ph), p-MeC6H4Hg(SO2-p-MeC6H4), PhHg(SO2-p-MeC6H4), p-MeC6H4Hg(SO2Ph), and C6F5Hg(SO2Ph), have been prepared by reaction of mercuric benzenesulphinate or p-toluenesulphinate with the appropriate diarylmercury compound in chloroform or methanol, and the first three compounds have also been obtained by reaction of liquid sulphur dioxide with diphenylmercury, di-p-tolylmercury, or phenyl-p-tolylmercury. Linkage isomers of phenylmercuric benzenesulphinate have been prepared. Isomer A, obtained from chloroform-pentane, is considered to be a monomeric O-sulphinato complex, and isomer B, obtained from cold acetone, methyl ethyI ketone, or methanol, to be an S-sulphinato complex. The isomers are readily interconverted. In chloroform, deuterochloroform, and acetone, at room temperature, only the O-sulphinato complex can be detected. The other arylmercuric arenesulphinates have the same structure as isomer A. Linkage isomers could not be isolated for these derivatives. However, there is evidence that p-MeC6H4Hg(SO2Ph) slowly isomerizes in the solid state to give the corresponding S-sulphinato complex. Thermal decomposition of PhHg-(SO2Ph) (both isomers), p-MeC6H4Hg(SO2-p-MeC6H4), PhHg(SO2-p-MeC6H4), and p-MeC8H4Hg(SO2Ph) gives sulphur dioxide and the corresponding diarylmercurycompound.