The present invention relates to compounds which are effective as catalysts for dismutating superoxide and, more particularly, the manganese or iron complexes of substituted, unsaturated heterocyclic 16-membered macrocyclic complexes that catalytically dismutate superoxide. It also relates to methods of using these complexes to reduce the concentration or the effects of superoxide, pharmaceutical compositions comprising these compounds or their metal complexes, and methods of treating conditions associated with excessive superoxide activity.