SUMMARY Twelve 1-week-old colostrum-deprived lambs inoculated with the RTS-42 strain of Mastadenovirus ovi 5 were killed and necropsied (2 lambs/day) on postinoculation days (pid) 2, 4, 6, 8, 12, and 21. Four noninoculated lambs were killed and necropsied (2/day) on pid 6 and 12. Virus was isolated from nasal secretions and feces on pid 1 to pid 6, from tracheal fluids and lung tissue of lambs necropsied on pid 2, 4, and 6, and from lung tissue from 1 lamb necropsied on pid 8. Virus was not recovered from liver, kidney, or small intestine of inoculated lambs or samples from noninoculated lambs. Serum antibody was first detected on pid 6 in the inoculated lambs. Noninoculated lambs remained seronegative. None of the lambs in the study developed clinical signs of infection although lesions were produced in the respiratory tract.