Formalinized vaccines prepared from the Nine Mile, Phase I, strain of C. burneti or purified preparations of the Phase I antigen initiate a state of delayed hypersensitivity in guinea pigs as determined by the in vitro migration inhibition system. This delayed hypersensitivity is directed against the protein as well as the carbohydrate component of the Phase I antigen. Guinea pigs that had recovered from Q-fever demonstrated a similar state of delayed hypersensitivity. Circulating antibody levels as determined by the microagglutination test were readily apparent in both infected and vaccinated animals.