System used to describe rejection for kidney transplants, with 6 diagnostic categories acute rejection, chronic rejection, hyperacute rejection, normal histology, borderline changes, and changes not related to rejection. Acute rejection grade I, moderate interstitial infiltrate with tubulitis but no vascular changes; grade II, moderate to severe interstitial infiltrate with severe tubulitis and possible mild to moderate intimal arteritis; grade III, severe intimal arteritis with fibrinoid necrosis, grade I, mild interstitial fibrosis with tubular atrophy; grade II, moderate interstitial fibrosis with tubular atrophy; grade III, severe interstitial fibrosis and tubular atrophy and loss.