The role of marine birds, mammals, turtles and fish as vectors of infectious agents of potential risk to humans can be examined from a variety of perspectives. The studies in this DAO Special include a broad survey of multiple agents and species, a sequencing study of Giardia intestinalis haplotypes known to be pathogenic to humans, an assessment of risks to humans working with marine mammals, a source tracking study using E. coli ribotypes, studies of regional Salmonella and Brucella epizootiology, a serology survey and a case report of a herpes simplex infection in a dolphin. Additionally, a recently published study (Venn-Watson et al. 2008; Dis Aquat Org 79:87-93) classifying pure cultures of bacteria from a captive dolphin colony also pertains to this theme. These studies raise the following questions: whether the presence of zoonotic agents in marine vertebrates represents a risk to other marine vertebrates, humans, or both; what are the routes by which these marine vertebrate zoonotic infections are acquired and circulated in the marine ecosystem; to what degree are such agents subclinical versus causes of overt disease in marine vertebrates; what are the subsets of the human population most likely to be affected by such infections; and which human health preventive measures would seem reasonable?