Experiments were conducted to characterize renal lesions in chickens induced by four strains of infectious bronchitis virus (IBV); each has been described as nephropathogenic. Those strains were also compared in vaccinated and unvaccinated older chickens for nephropathogenicity. The younger birds were much more susceptible to the nephritogenic effects of the strains. All four strains produced acute renal changes consisting of tubular damage and interstitial inflammatory cell infiltration and edema. Although both cortex and medulla were involved, the latter was generally affected more severely. The Holte strain proved to be the least pathogenic, followed by the more pathogenic Gray and Italian strains and finally by the Australian strain. All four strains produced similar chronic renal changes in unvaccinated birds, with no correlation to the severity of lesions seen at the acute phase. Chronic active and inactive types of interstitial nephritis were seen at the chronic phase. Vaccinated birds challenged with the Australian strain had the highest prevalence of the chronic active type of interstitial nephritis. The implication of renal viral persistence in the development of chronic active interstitial nephritis is discussed.