H-1 virus infection of hamsters has been shown to produce runting, microcephaly, cranial lacunae, and deformed teeth in animals inoculated during the suckling period and to cause various abnormalities, including skeletal defects, in embryos infected transplacentally. To explore the pathogenesis of these effects of viral infection on bone, the response of embryonic hamster tibiae in organ culture to inoculation with the H-1 strain of picodna virus was studied. This system made possible the direct observation of the reaction of bone to virus in a regulated environment. During a period of 7-17 days after inoculation the following observations were made: (a) H-1 virus was found to infect and replicate in bone. (b) Infected bones became more translucent, slender, and elongated than control bones. (c) Bone growth as measured by increase in wet weight was reduced in infected tibiae. (d) Infected bones showed periosteal and perichondral degeneration and diminished deposits of subperiosteal bone. It was concluded that the skeletal abnormalities which develop in embryonic and suckling hamsters after H-1 virus inoculation are the direct result of viral replication in bone, and that indirect phenomena such as those associated with chronic infection need not be postulated to explain the deformities seen in these animals.