72 percutaneous diagnostic renal biopsies were performed on 53 recipients of renal allografts from cadavers with deterioration of the graft function. 40 patients received cyclosporine (CsA) and 13 Azathioprin with steroids (conventional immunosuppression). All biopsies were carried out under sonographic control. The echo patterns of the grafts were evaluated prior to the procedure. In 63 cases (87.5%) enough material could be obtained for histologic examination. The sonographic diagnoses were compared with histological results. In the sonographic detection of allograft rejection sensitivity was 80.85%, and specificity 56.25%. Grafts with symptoms of CsA-nephrotoxicity did not seem to produce a characteristic sonographic echo pattern. Macrohaematuria occurred after 9 biopsies (12.5%). A graft loss was not observed; in one case a temporary percutaneous nephrostomy had to be carried out. We conclude that sonography alone is not sufficient to diagnose parenchymatous changes in the graft. To obtain satisfactory long-term results biopsy is necessary. Under sonographic guidance the risk of percutaneous biopsy is minimal.