The pathology and infectious agents associated with several outbreaks of clinical tenosynovitis in poultry were investigated. Staphylococcus aureus were recovered from tendon tissue of from 51.9% to 97.8% of affected chickens in different outbreaks of the disease. S. aureus were also present in the liver and heart blood and were considered to contribute to the high mortality observed following occurrence of clinical tenosynovitis in individual chickens. Bacteria other than S. aureus were also recovered but in a much lower proportion of chickens than was S. aureus. Adenoviruses and reoviruses were also recovered from tendon tissue of chickens with a concurrent bacterial infection. Although the pathology observed in clinically affected chickens was suggestive of a bacterial aetiology it is hypothesised that the tenosynovitis outbreaks investigated were due to an early viral infection which normally remained subclinical and that secondary infection with bacteria, particularly S. aureus, was responsible for the development of clinical signs.