We briefly review the pathology, epidemiology and molecular biology of cetacean viruses (including morbilli, papilloma and pox) and Brucella spp. encountered in South America. Antibodies against cetacean morbillivirus were detected (by iELISAs and virus neutralisation tests) in SE Pacific and SW Atlantic delphinids. Morbilliviruses are possibly enzootic in Lagenorhynchus obscurus and offshore Tursiops truncatus from Peru and in Lagenodelphis hosei from Brazil and Argentina, but no morbillivirus antibodies were found in inshore small cetaceans. Papillomaviruses cause genital warts in at least three odontocete species in Peru. Two Phocoena spinipinnis papillomaviruses (PsPVs) were found in warts of Burmeister’s porpoises; one (PsPV-1) was cloned and characterized. Half of porpoises had developed genital warts, while in 10% of males the lesions were sufficiently numerous and severe to at least hamper, if not impede, copulation. High titers of cowpox virus neutralising antibodies were detected in Peruvian D. capensis, T. truncatus, L. obscurus and P. spinipinnis in 1993-1995. The high prevalence of orthopoxvirus neutralising antibodies with high titres indicates common infection by poxviruses antigenically related to cowpox virus, the probable causative agents of tattoo skin disease. Cetacean poxviruses may cause significant mortaliy among neonates and calves unprotected by maternal immunity. In Peru, Brucella spp. antibodies were detected (competitive ELISA) in D. capensis, T. truncatus, L. obscurus and P. spinipinnis. Brucellosis is likely enzootic in the latter two species, and may lead to orchitis and bone lesions in L. obscurus and D. capensis. The enzootic circulation of brucellae in L. obscurus and P. spinipinnis may constitute a measurable limiting factor among the environmental variables affecting population dynamics. Also, widespread Brucella spp. infection in several Peruvian odontocetes has public health implications (zoonosis), considering frequent manipulation of carcases and consumption of meat. Extrinsic anthropogenic factors may not only exacerbate the consequences of viral infections on the health of a particular individual, but also operate at the population level.