Histological examination was conducted of kidneys made available from a previous experiment, which investigated different infectious bronchitis virus (IBV) vaccination protocols for laying hens (Sulaiman et al., 2001). Histological changes were used as a possible measure of the level of protection afforded by different vaccination protocols. Kidneys were examined from ISA Brown cockerels that were vaccinated at day old or two weeks by coarse spray, eye-drop or drinking water and then revaccinated by the same routes at 8 weeks. A control group of unvaccinated birds was also maintained. Ten birds from each group were challenged at 11 weeks of age with T-strain infectious bronchitis virus. Five birds from each group were euthanased at one, two and three weeks post exposure and the kidneys preserved for histological examination. At each time interval following exposure to T-strain IBV, kidney sections were prepared from the birds with the largest and smallest kidneys (as a percentage of body weight), stained with haematoxylin and eosin, and examined for histological changes (a total of 6 birds per treatment, 2 kidneys per bird, 3 divisions per kidney). Also, the cranial divisions were examined for all 5 birds in vaccinated groups that showed histopathology.