The prevalence of precipitating antibodies to avian adenoviruses in 1431 diagnostic serums originating from poultry farms in the northern half of the North Island was 34.7%. Precipitating antibodies were first detected in birds 8 weeks of age and the prevalence increased steadily with age until the birds were 12 months old. The majority of poultry farms (74%)had serological evidence of the presence of AAV.