Phenylnitrenium ions are generated from phenylhydrazines by treatment with AlCl 3. Reaction of a phenylnitrenium ion with arenes results in both aromatic N-substitution and C- substitution. In contrast, an N-methylphenylnitrenium ion undergoes exclusively aromatic C- substitution. Reaction of a phenylnitrenium ion with arenes present only in slight excess produces anilinated products in moderate to good yields.