Husbandry procedures were developed for the gray short-tailed opossum (Monodelphis domestica) based on experience with several colonies that were self-sustaining for up to 4 years (five generations). Individual adult animals (80-155 g) were maintained in modified single rat or guinea pig cages, although larger cages with floor areas of at least 2,000 cm2 were required for breeding. Diets consisted primarily of ground meat, dried milk powder, wheat germ, and vitamin supplements. Switching males in the breeding pairs stimulated reproductive activity. Monodelphis domestica was found to be hardy, tractable, and able to reproduce throughout the year under laboratory conditions. This species is proposed as a practical marsupial model for biomedical research.