. This RO3 is an application to the Fogarty International Center AIDS International Research and Training Program. The objective of this collaborative study between California Regional Primate Research Center (CRPRC) and the Institute of Primate Research (IPR) in Kenya is to define the biology of simian immunodeficiency virus (SIVagm) in a natural host, the African green monkey (AGM), Cercopethecus aethiops. It is noteworthy that the AGMs have not been heavily used in AIDS and SIV research. Despite the fact that large numbers of African green monkeys (AGMs) in the wild and captivity are persistently infected with SIVagm, they do not display clinical signs of simian AIDS, unlike Asian macaques infected with SIVagm. This observation has led to suggestions that SIVagm and its natural host have co-evolved into a nonpathogenic relationship. This study will therefore seek to clarify the biology of SIVagm in the AGM by defining (a) the biology of SIVagm in naturally infected AGMs from the wild, (b) the biology of SIVagm in experimentally infected captive AGMs, (c) the role of routes of virus inoculation on SIVagm pathogenesis and (d) the biology of SIVagm on immunologically immature host, the AGM newborn. The authors suggest that AGMs provide an excellent model to seek answers to these questions, because (i) over one third of wild and captive AGMs are SIV-infected (ii) AGM-infection with SIVagm is nonpathogenic and (iii) large numbers of AGMs are available for the proposed study. This study therefore proposes to use naturally infected AGMs, intravenously or mucosally infected adult AGMs and newborn AGMs to examine and define (a) anti-SIV cytotoxic T-cell lympocyte (CTL) and antibody responses, (b) viral burden in the peripheral blood and plasma, (c) the SIVagm distribution in tissues and organs.