The reaction of crosslinked poly(styrene-4-vinylpyridine), containing 42–44% of pyridine rings, in chloroform suspension with a mixture of hydrogen chloride and iodine chloride formed the cross-linked poly{styrene-[4-vinyl pyridinium dichloroiodate (I)]}(PSVP). Better results were obtained when cross-linked poly[styrene-(4-vinylpyridinium chloride)] was prepared first, followed by the reaction with an equivalent amount of iodine chloride. Benzene and naphthalene derivatives were quantitatively converted with cross-linked PSVP into monoiodo substituted products of very high purity, while reaction of greater amounts of polymeric reagents with 3-amino- and 3,5-diaminobenzoic acid gave the tri-iodo derivatives. On the other hand, reaction with dimethyluracil led to the 5-iodo derivative, while in the reaction with 8-hydroxyquinoline the 5,7-di-iodo derivative was formed. In the case of 5-chloro-8-hydroxyquinoline, iodination occurred at the 7-position, while on reaction with 4-pyridone 3,5-di-iodo-4-pyridone was formed.