In this study antigen independent factor in the pathogenesis of chronic rejection of organ transplants was examined. Kidney isografts and allografts were transplanted orthotopically into bilaterally nephroectomized rat recipients and studied functionally, morphologically and immunohistologically, at serial intervals up to 52 weeks after transplantation. Allograft recipients developed progressive proteinuria after 12 weeks, with gradual renal failure ultimately leading to death. At the same time, morphological changes, including progressive arteriosclerosis and glomerulosclerosis, tubular atrophy and interstitial fibrosis, developed. Immunohistologically, macrophages infiltrated glomeruli during this period and cytokines became unregulated. Our results showed that antigen independent functional and morphological changes occurred in long term kidney isografts and mimicked those appearing much earlier in allografts that reject chronically. Initial injury and extent of functioning renal mass is suggested to be important factor for such late changes. In this study antigen independent factor in the pathogenesis of chronic rejection of organ transplants was examined. Kidney isografts and allografts were transplanted orthotopically into bilaterally nephroectomized rat recipients and studied functionally, morphologically and immunohistologically, at serial intervals up to 52 weeks after transplantation. Allograft recipients developed progressive proteinuria after 12 weeks, with gradual renal failure ultimately leading to death. At the same time, morphological changes, including progressive arteriosclerosis and glomerulosclerosis, tubular atrophy and interstitial fibrosis, developed. Immunohistologically, macrophages infiltrated glomeruli during this period and cytokines became unregulated . Our results showed that antigen independent functional and morphological changes occurred in long term kidney isografts and mimicked those appearing much earlier in allografts that reject chronically. Initial injury and extent of functioning rena l mass is suggested to be important factor for such late changes.