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A number of researchers have explored the relationship between companion animal ownership and human physical and psychological health. Results have been inconclusive, with positive, neutral and negative effects variously reported in the literature. Furthermore, the possible mechanisms of any influence are frustratingly unclear. A number of conceptual and methodological weaknesses have hampered progress in our understanding of how companion animals may impact upon human health. The two evidence gaps discussed in this paper, with suggestions for needed next steps, are: (i) a preponderance of anecdotal reports and cross-sectional research designs; and (ii) failure to control for a host of other known influences on human health including health habits, level of attachment to the companion animal and human social supports. Finally, an example of these gaps is provided in relation to the literature on the effects of animals on elderly nursing home residents.