A review of data on the antigen B of Taenia solium (AgB) is presented. The biochemical, immunological and physiological properties of AgB are discussed in the context of the host-parasite relationship. It is proposed that AgB facilitates survival of cysticerci by impairing augmentation of the host inflammatory response through the inhibition of the classical pathway of the complement cascade. In this way, AgB not only allows evasion of the host immune attack but also decreases the host-parasite confrontation, facilitating their coexistence.