Numerous species of birds are natural hosts of C. psittaci and have been implicated as sources of certain strains that cause disease in other vertebrate species, notably those producing psittacosis or ornithosis in humans [1]. Although direct evidence of their involvement in the transmission of chlamydiae to other mammals, especially domesticated ruminants, has not been reported, a careful examination of this possibility is justified [1]. When inoculated parenterally, polyarthritis-producing chlamydiae of ovine origin affected leg joints of turkeys, and abortion-producing chlamydiae of ovine origin was infectious for pigeons and fatal for sparrows [2]. However, several species of small wild birds (three of which were used in the experiments reported here), when inoculated perorally with C. psittaci of turkey origin, seroconverted (36%) and shed the organism (79%) [3]. Therefore, the present study was undertaken to determine whether strains of C. psittaci from domesticated ruminants would infect, multiply in, or be shed by these wild birds. The results indicate that these species of birds are not natural hosts or biologic vectors of these strains. However, considering the heterogeneity of Chlamydia species, certain birds may harbor strains that are associated with naturally occurring infections in some animals. The results also are additional evidence of the more restricted host range of mammalian Chlamydia species as compared to that of avian isolates.