The immunology and histopathology and the distribution of viral antigen in infections with chicken infectious anaemia virus (CIAV) and inclusion body hepatitis virus (IBHV) were compared in the broiler offspring of CIAV-vaccinated meat chicken breeders versus those in the offspring of breeders naturally exposed to field CIAV. No significant difference in the humoral antibody level specific for CIAV was observed between 5 and 33 weeks of age in the two breeder groups (p > 0.05). The maternal humoral immunity to CIAV in the day-old offspring of the groups did not differ significantly (p > 0.05). The humoral immunity to CIAV at 40 days of age indicated an absence of clinical signs of CIAV in the broiler offspring of both groups of breeders and this was associated with mean serum thymulin levels in offspring of both groups not differing significantly at 1 or 40 days of age. Histopathological and immunofluorescence observations did not differ significantly in the offspring of either group by CIAV or IBHV.