In this study the incidence and the development of acute renal failure (ARF) in heart transplant recipients is presented. Among the thirteen heart transplant recipients eight of them developed oliguric or nonoliguric ARF. Besides the known factors such as actual condition of the patient, kidney function, peri and post-operative compromised circulation, our results demonstrate the significance of postoperative cyclosporin concentration in combination with the use of other drugs. The results also show the importance of the way cyclosporin has been administrated. The parenteral route of appliance is connected with the greater risk of higher drug concentration in the plasma than the peroral one. In connection with this is the higher incidence of adverse reactions to cyclosporin given parenterally. In addition to ranitidine and captopril, which have been mentioned earlier, the findings of our study indicate that greater attention has to be paid to the treatment with ketoconazol given in combination with cyclosporin, since it results in decreased cyclosporin clearance. Other nephrotoxic drugs like amphotericin also increase the possibility of renal lesions. The incidence of acute renal failure in this group of patients is high. Our data suggest that the reasons for the development of ARF are multifactorial. These data further suggest that a reasonable way to solve nonoliguric form of acute renal failure is to maintain the "internal balance" and that it is not necessary to perform extracorporeal elimination of nitrogen substances, if there are no additional complications (i.e. gastrointestinal bleeding).(ABSTRACT TRUNCATED AT 250 WORDS)