A case of Chlamydia B (psittacosis) endocarditis is described in a patient with no known previous valve disease. After mitral valve replacement afall in Chlamydia B antibody titre occurred. At repeat mitral valve replacement five months later for a paravalve leak no evidence of continuing endocarditis was present. Direct confirmation of infection in the patient's apparently healthy budgerigar was obtained. Aspects of the pathogenesis, diagnosis, and treatment are discussed.