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Liver collected aseptically from broiler chickens suffering from natural outbreaks of hydropericardium syndrome was homogenised in phosphate buffered saline (1:5) or normal saline (1:10). A dose of 0.25 ml of 800 g supernatant (inoculum S) in the first case or homogenate without centrifugation (inoculum T) in the second case was injected subcutaneously into 12- to 15-day-old broiler chickens. Lesions similar to natural outbreaks of the syndrome appeared in 2 to 5 days. Inoculum S inactivated with 0.1% formalin for 24 h (Vac S) or inoculum T inactivated with 0.5% formalin for 72 h (Vac T) was injected into commercial broiler chickens at 10 or 15 days of age. The birds were challenged with inoculum S or inoculum T at 20 or 25 days of age. Experimentally both vaccines gave satisfactory protection, but under field conditions, Vac T was superior.

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1. The concentrations of 17 beta-oestradiol (E2) and progesterone (P) were determined in the plasma of layer breeder hens at the end of their first laying season, in relation to neoplasms of the oviduct, including magnum tumours and leiomyomas. 2. The plasma concentration of E2 was higher in tumorous than in non-tumorous hens indicating it may be involved in the development of oviduct tumours. 3. The plasma concentrations of P in tumorous and non-tumorous hens were not significantly different, suggesting no active role of P in the aetiology of the tumours. 4. The E2: P ratio was higher in tumorous than in non-tumorous hens. This ratio could be of value in predicting hens at risk of developing oviduct tumours.