Two inactivated vaccines were prepared against hydropericardium syndrome. T
he vaccine prepared from liver homogenate extracted with chloroform, inacti
vated with formalin and adjuvanted with liquid paraffin was highly effectiv
e against challenge in chickens aged three, five and seven weeks. Seroconve
rsion following vaccination and challenge was assessed by the agar gel immu
nodiffusion test The inactivated oil emulsion vaccine was highly effective
against the syndrome in both experimental trials and field trials.