Guinea pigs inoculated with an aqueous suspension of killed Toxoplasma developed dye test antibody but not complement fixing antibody. When an adjuvant was combined with the antigen both antibodies developed and considerable immunity resulted. The antigen was apparently associated with the whole Toxoplasma rather than its extracts, even though the latter actively fixed complement. Whereas convalescent animals were able to resist an intracerebral inoculation of Toxoplasma, the vaccinated animals were immune only to intradermal and intraperitoneal inoculation. It has been shown that Toxoplasma are disseminated through the guinea pig even in the presence of very high levels of complement fixing antibody.