The phylogenetic relationship of nonhuman primates to man implies that many of these animals could serve as surrogates for studies of diseases of man. Many nonhuman primate species are susceptible not only to viruses of human origin but also to nonhuman primate viruses that are counterparts of viruses of man. All monkeys and great apes do not respond similarly to an antigenic stimulus. Some agents are highly pathogenic for one species and completely innocuous for another. For example, poliovirus causes disease and fatalities in great apes, but picornaviruses given orally cause few lesions in most nonhuman primates. Other enteroviruses (coxsackie-, echoviruses) have caused disease in nonhuman primates. It is difficult to separate viruses into distinct categories according to their anatomic affinities. Many viruses not considered to be enteric may be recovered from the intestinal tract. Adenoviruses, both human and nonhuman strains, which are not considered enteric viruses, nonetheless are recovered frequently from the intestinal tract. Adult animals show little evidence of disease, with the possible exception of diarrhea, after adenovirus infection. Newborns, however, may respond with a fatal pneumoenteritis. Adenovirus may be associated with diseases in organs other than the intestines. The reoviruses, which may be recovered from the intestinal tract, also are generally innocuous. Rotaviruses as pathogens in nonhuman primates are presently under study, and it is suspected that rotaviruses of man may produce experimental disease in nonhuman primates. Production of diabetes by several of the enteric viruses has been suggested but not demonstrated conclusively.