Zaire Ebola virus infection in macaques causes a fatal disease with a pathogenesis similar to that in humans. During several independent therapy studies, we noted altered tissue tropism in 6 rhesus macaques that survived longer than those with a typical disease course. The mean time to death for these 6 macaques was 21.7 days, which is significantly longer than the average mean time to death of 8.3 days for 20 untreated historical control animals. In addition to living significantly longer, these 6 animals exhibited a variety of deteriorating clinical signs with pathologic findings that were not seen in the untreated control animals, as well as the presence of viral antigen in the brain, eye, pancreas, thyroid, and lung. We suggest that treatment extended the time course of the disease and permitted the virus to infect tissues not usually affected in the typical model.