Brain homogenates (10% w/v) from five of seven kuru patients inoculated intracerebrally (i.c., 0.1 ml) into marmosets (Saguinus sp.) induced a rapidly progressive CNS disease 26, 31, 36, 76 and 94 months postinoculation. Serial marmoset passages of kuru were accomplished by i.c. inoculation of neonatal marmosets with brain homogenates from marmosets with experimentally induced kuru. The incubation periods ranged from 1.5 to 11 months (average 7.3) in 19 animals, 20-25 months in four animals and greater than 26 months in two animals. Symptoms and brain lesions of the induced disease were compatible with kuru as observed in humans and other nonhuman primates. Creutzfeldt-Jakob disease (CJD) has been induced by i.c. inoculation of marmosets with brain homogenates from two of four human CJD patients with incubation periods of 43 and 54 months and is in serial passage.