In this brief review, the authors summarize the state of knowledge on chlamydial infections in birds and mammals, in particular those occurring in domestic animals. Chlamydia psittaci is responsible for a variety of syndromes in veterinary medicine, some of which may be of great interest in comparative pathology (polyarthritis, conjunctivitis, . . .). The frequency of latent infections, the difficulties involved in the diagnosis and control of chlamydial infections and the transmissibility of C. psittaci to man pose a number of problems for the veterinarian, both in terms of animal medicine and in terms of his role in public hygiene.