Synthesis of diaryliodonium salts from ortho- or para-substituted iodoso-aryl acetates carrying ortho,para-directing substituents proceeds with both ortho- and para-substitution, the relative amounts of which depend on the substituents in the original aryl system. No meta-substitution has been found. Direct synthesis of iodonium salts from the aryl compound (toluene and chlorobenzene have been examined) also gives a mixture of isomers (p,p′-, o,p′-, and o,o′-); the ratios of o- to p-substitution have been deduced from an analysis of the cleavage products of the iodonium salts.