Our recent review indicates that numerous factors are involved in selecting an animal model for the study of human disease processes. These include: anatomic, neurologic, physiologic, and pathologic parameters, concept of discrimination, volume of knowledge available, and costs. Regarding costs, data was collected from twelve medical research institutions in relation to the eight animals selected for comparative cost analysis: rhesus monkey, cynomolgus monkey, Sprague-Dawley (S.D.) rat, dog (mongrel), cat (mixed breed), swine (piglet), guinea pig, and rabbit. Biologically, the choices are vast and depend upon the investigator and the experimental design. Economically, pricing is a substantial constraint that varies widely and is institutionally dependent. Furthermore, within the same institution, costs differ according to the source of funding (e.g., private, federal, state, or institutional). However, if the investigator carefully considers these biologic and economic factors, it is possible to select an appropriate animal model.