White Leghorn chicks without and with maternally derived antibodies (MDA) to infectious bronchitis virus (IBV) and broiler chicks with MDA were vaccinated at 1 day of age either with H120 vaccine, combined H120 and D274 vaccines or with a non-commercial attenuated strain derived from the virulent Belgian nephropathogenic IBV strain, B1648. Protection following challenge with virulent B1648 was assessed 4 weeks later by virus isolation from the trachea, antigen detection in the kidney by immunofluorescence and mortality rates. Vaccination with either homologous or heterologous vaccines reduced the duration of virus replication in the trachea of all groups compared to unvaccinated controls. Homologous vaccination reduced the incidence of virus replication in the kidney. Heterologous vaccination (H120 to D274) did not reduce kidney infection in the MDA + groups; however, partial kidney-protection was found in the MDA - group. There was no correlation between serum antibody titres measured by ELISA and the degree of kidney protection.