Because of their close phylogenetic relationship, human and nonhuman primates share susceptibility to many pathogens which do not affect lower animals. This similarity, which makes them invaluable models for studying human infectious diseases, also makes primate animals potentially dangerous to work with. The biohazards inherent in the use of nonhuman primates in biomedical research are zoonoses, injuries, and infectious agents introduced by study protocols. This review addresses the various kinds of parasites, fungi, rickettsiae, spirochetes, and viral agents found naturally occurring, or experimentally induced, in nonhuman primates with reference to measures for preventing spread among the animals or to personnel.