Australian Centre for International Agricultural Research Canberra 2003Infectious diseases in rodent populations are discussed from the twin viewpoints of their threat to human health and their role in rodent population dynamics. This is not, though, a definitive or exhaustive review, but an attempt to identify important and/or interesting themes. As regards human health, most recent attention has been directed at emerging infections, but some rodent-reservoir zoonoses are ‘sleeping giants’ that may awake at any time. Many human infections are never assigned an aetiological agent, and the ‘sources’ of many human pathogens remain unknown. Rodent-reservoir zoonoses may be important in both cases. In some cases, the economic damage caused by a pathogen may demand action even though medical effects, by most measures of public health, are trivial. Finally, the ‘hottest’ topic in human infectious diseases is bioterrorism. Rodent-reservoir zoonoses account for many of the apparently prime candidates. As regards rodent populations, four topics are addressed, focusing on work from our group at Liverpool—the effects of endemic pathogens on host fecundity as evidenced by experimental studies; their effects on host survival as evidenced by the analysis of field data; analyses of the transmission dynamics of infection and the light these throw on common theoretical assumptions; and the possible role of pathogens in microtine rodent cycles. Finally, at the interface between rodent populations and human health, the importance of distinguishing between reservoir, liaison and incidental hosts is emphasised; the contrasts between controlling zoonotic infections and other human infections are discussed; and a connection between contrasting types of rodent zoonosis and the nature of pathogen virulence is suggested.