In this review of the literature concerning the immunology of animal and human cysticercosis, emphasis is placed on whether previous exposure to the antigen confers protection to the host. Statistical analysis of the published data indicates that immunized animals have a lower risk than non-immunized animals of contracting cysticercosis, there being large variations within and between different host-cysticercus relationships. There is no indication as to which antigen is best for immunization but, although live parasites in all stages of development, or extracts, appear to give protection, embryos, eggs, and excretions are most frequently used. Antibodies appear to be the principal mediators of resistance, but the action seems to be only upon very young larvae, while fully grown cysticerci are unharmed. Several immunological methods are valuable in the diagnosis of cysticercosis, the choice depending more on the purpose of the study than on differences in their ability to discriminate between healthy and sick. The presence of anticysticercus antibodies in the serum of up to 50% of human patients indicates that human vaccination may be possible in high-risk areas; the remaining patients pose an interesting problem open to speculation and research on immunological evasion, immunodepression, and the existence of serotypes.