Despite known morphological criteria of kidney allograft rejection a definite diagnosis of interstitial rejection in not possible in each case. Therefore, by an enzyme histological differentiation of infiltrating cells in the transplant biopsy specimen this problem should be solved. It was used the PAP method against pan T lymphocytes, T4 and T8 lymphocytes, monocytes and granulocytes. An acute interstitial rejection can be verified if 1. the number of lymphocytes and their subpopulations did increase over the maximum values, 2. without vascular rejection is the T4/T8 ration less than 1 and 3. in the presence of vascular rejection is the T4/T8 ratio greater than 1. Additional information about cyclosporin injury or viral infections may be possible. It is possible increase markedly the rate of safer diagnosis by immunohistological differentiation of infiltrating cells.