The authors evaluated the pathomorphologic alterations of removed and reperfused dog kidneys by means of light and electronmicroscopic examination. In each sample the following reversible signs were found: Hypereosinophilia (HE), Hydropic dystrophy (HD), Nuclear polymorphism (NP), Epithelial desquamation (ED), Brush border lesion (BBL), Single cell necrosis (SCN), Total tubular epithel necrosis (TTEN), Interstitial edema (IE), Perivascular edema (PE). The irreversible signs were: Basement membrane rupture (BMR), Cellular infiltration (CI), Glomerular mesangial matrix expansion (GME) and vascular lesions (VL). The most severe and mostly irreversible alterations occur in the 54-72 hours after harvesting. The authors emphasize the significance of basement membrane rupture, because the impossibility of tubular epithelial regeneration, the cellular infiltration due to its fibrogenic effect, glomerular lesion because it makes decrease the glomerular filtration rate, proceeding juxtaglomerular cell proliferation and hypertension through renin-angiotensin mechanism and vascular lesions causing renovascular hypertension and tubulopathy. The authors believe that reperfusion injury is very important factor in kidney allograft survival. Its mechanism is similar to the normal necrosis pathway, but the timing is delayed. Further investigations are needed to understand what specific alterations may occurred under blood circulation in the host to reveal more exact cause of primary graft failure after transplantation.