The agent causing Jembrana disease, an enzootic disease of Bos javanicus (Bali cattle) occurring in Bali, Indonesia, was shown to occur at high titres in the blood of animals during the febrile period of the disease and to persist in cattle for 25 months after clinical recovery. During the febrile period of the disease, most of the infectious agent appeared to be associated with the plasma fraction of whole blood. There was a linear relationship between the number of organisms inoculated into susceptible Bali cattle and the incubation period, which varied from 4.5 to 12 days. Seventeen of 18 animals in which Jembrana disease had been experimentally induced up to 22 months previously did not develop clinical signs when re-challenged with the infectious agent. Ongole cattle (Bos indicus), Friesian cattle (Bos taurus), buffaloes (Bubalus bubalis) and pigs, but not sheep or goats, developed a mild febrile response, but no other overt clinical signs of the disease after inoculation with the Jembrana disease agent. Ongole and Friesian cattle, buffaloes, and sheep developed a persistent infection after inoculation; the infectious agent persisted in blood or spleen for at least 9 months in buffaloes and for shorter periods in the other species.