Five species of mammals and 3 species of birds passed polyhedral inclusion bodies (PIB) of the gypsy moth nucleopolyhedrosis virus (NPV) through their alimentary tracts in amounts great enough to kill gypsy moth larvae in bioassays. Opossums and raccoons passed roughly 5% of the PIB administered by intubation while white-footed mice, a short-tailed shrew, and southern flying squirrels passed 2.3, 1.8, and 0.05%, respectively. House finches and a red-winged blackbird passed close to 15% of the PIB administered, whereas mourning doves passed 0.05%.All the birds, as well as the shrew and squirrels, passed the PIB within 6 h of intubation. The white-footed mice passed PIB within 18 h of intubation, while it took the raccoons 22, and the opossums 70 h to eliminate PIB from their alimentary tracts.It is concluded that both mammals and birds pass significant amounts of NPV, and that both groups have features which contribute to their ability to passively transport NPV within the environment.