Genetic studies of tuna began with immunological techniques on blood groups and were followed by immunoelectrophoresis and electrophoresis with improved histochemical staining techniques. These increased our ability to study polymorphisms in soluble proteins and enzymes not only in blood but also in tissues or organs in tuna. Six species of tuna have been studied for polymorphisms: albacore, Thunnus alalunga; bigeye tuna, T. obesus; yellowfin tuna, T. albacares; bluefin tuna, T. thynnus; southern bluefin tuna, T. maccoyii; and skipjack tuna, Katsuwonus pelamis. Progress in the studies of the polymorphisms and their application to subpopulation identification was reviewed. Some problems in methodology in identifying subpopulations arose from the studies and the possible aids for their solution were discussed.