The majority of parasitic infections of man are of zoonotic origin. In
a conceptual framework for the incrimination of mammalian reservoir h
osts, these are defined as being essential to the maintenance of paras
ite suprapopulations. A series of guidelines are given for the accumul
ation of the relevant information. It is proposed that mammal ecologis
ts can contribute significantly to the understanding of medically impo
rtant zoonoses.