The participation of halogen substituted 3-aryl-phthalazinium-1-olates in cycloaddition reactions were stud ed with various olefinic and acetylenic dipolarophiles. The betaines gave the expected cycloadducts with vinyl acetate, vinyl phenyl ether, and vinyl phenyl sulfide. However, two isomeric products were obtained with diethyl acetylenedicarboxylate. One of them was the normal expected cycloadduct and the other one was the rearranged cycloadduct. On the other hand, reactions with phenyl acetylene produced only the rearranged cycloadducts.