The aetiology of an outbreak of haemorrhagic syndrome (HS) in a commercial broiler flock was examined. At a rearing farm, 596 of 6376 chicks (9.3%) in a flock were culled with depression and increased mortality from 12 to 26 days of age, with a peak at 16 to 19 days of age. Most of the affected chicks examined had haemorrhagic lesions of the muscles, atrophic changes of the lymphoid organs and aplastic bone marrow. Chicken anaemia agent (CAA) was isolated from the livers of all the 21 chicks examined. No fowl adenovirus was isolated. The present field case of HS coincides fairly well with the disease which is produced experimentally by CAA.