The rickettsial agents of American and Australian Q fevers persist in various tissues of guinea pigs and are present in their urine for considerable periods after defervescence. In a test with American Q fever lasting 54 days after inoculation, the rickettsia was recovered from the kidney for 40 days (the duration of the expt.), from the spleen for 20 days, from the liver, lungs, and brain for 15 days, and from the urine for 18 days after the last day of fever. In 2 tests with Australian Q fever, which each continued for 120 days after inoculation, the rickettsia was found present for at least the following approx. periods after defervescence: kidney and spleen, 110 days (the duration of the expt.); liver, 50 days; seminal vesicle and testes, 90 days; brain, 5 days; lungs, 20 days; and in the urine for 100 days. The persistence of the rickettsia of Australian Q fever in the seminal vesicles suggested that infected [male][male] might transmit the disease to normal [female][female] during copulation. 9 tests with the American disease and 10 with the Australian disease to obtain evidence on this point were all negative except one, the result of which was uncertain. The data from these tests suggested that both diseases affect pregnant animals more severely.