Infectious yolk sac suspensions were used to initiate agar tissue cultures using chick embryo tissue. These cultures grown at 35[degree] C for 8 days are usually rich in intra and extra cellular rickettsiae. The organism appears larger and plumper than those found in yolk sac cultures. Infectivity of agar tissue cultures for mice varies from 10-7 to 10-8.5. These cultures were inactivated by merthiolate or formaldehyde. When these vaccines were given intraperit. and the mice challenged by the same route, a protection of from 5,000 to 32,000 M.L.D. was induced. Neither normal chick tissue nor epidemic typhus vaccine is capable of inducing a resistance to scrub typhus. The effect of a booster inoculation was marked. The induced resistance increased from 7,950 to 80,000 M.L.D. in one expt. and from 25,000 to 250,000 M.L.D. in another.