Protection inducing antigens or parasites of the genus Plasmodium are described. The antigens have an apparent molecular weight of 1.8 to 2.5.times.10.sup.5 and are associated with the membranes of the erythrocytic schizont forms of the parasite. The antigens may be incorporated into vaccines and used for the inducing of immunity into susceptible vetebrate hosts including humans. Methods for the preparation of the antigens are also described.