Gray short-tailed opossums (Monodelphis domestica) are small marsupials, which have recently become the subjects of numerous laboratory investigations. While these opossums have well-developed olfactory systems and complex scent-marking behaviors, the significance of their use of odors in conspecific communication is still poorly understood. Investigation of body odors by male and female opossums was examined in the present study. Males investigated flank and urine odors of nonestrous adult females significantly more than controls, but not urine from sexually inexperienced juvenile females or urine of females at cytological estrus. Since in this species females have an induced estrus, it would be advantageous for males to investigate and follow the odors of urine of diestrous females, which become receptive in proximity to males. Female opossums investigated odors of male mandibles and suprasternal glands significantly more than controls but not odors of male urine. We suggest that the use of glandular secretions is more common and more effective than urine for intraspecific communication between gray short-tailed opossums: In the semiarid conditions inhabited by the opossums, glandular secretions are less volatile and are effective for longer periods than urine and would be of greater value in intraspecific communication if, as suggested in the literature, these opossums are nomadic and meet one another infrequently.