Introduction: Endocrine alterations associated with chronic renal failure have been reviewed recently. Some of these alterations are of clinical relevance. The aim of this study was to investigate the effect of renal transplantation on the endocrine system of the adrenal gland of the transplant recipients. Methods: The serum angiotensin-converting enzyme (SACE), plasma renin (PR) and plasma aldosterone (PA) were examined in 30 patients before and after renal allotransplantation. Additionally measured parameters were blood pressure, serum creatinine, potassium, sodium, the duration of dialysis and immunosuppressive medication. Results: Six weeks after renal transplantation, serum creatinine decreased from 820.07 ± 172.01 to 138.12 ± 67.54 µmol/l. In the same periode, serum potassium decreased from 5.42 ± 0.89 to 4.17 ± 0.42 mmol/l. PA and PR decreased from 1,150.84 ± 976.06 to 233.52 ± 217.07 µmol/l, and from 121.07 ± 100.12 to 26.16 ± 10.86 µU/ml, respectively. SACE decreased from 0.21 ± 0.21 to 0.13 ± 0.11 µmol/l. No significant correlation was seen with blood pressure, serum sodium, the duration of dialysis and immunosuppressive drugs. Additionally, 2 patients with acute renal graft dysfunction showed significant increases in PR and PA. After successful treatment both levels declined very quickly to prerejection levels. Patients after binephrectomy show no elevation in PR (5–47 µU/ml) or PA (21–416 µmol/l) neither before nor after renal transplantation. Conclusions: We conclude that renal transplantation has profound effects on the recipient’s renin-angiotensin-aldosterone system. Because of the rapid depression after renal transplantation, it does not appear to be involved in the pathogenesis of post transplantation hypertension but may reflect a role for repair processes after renal allotransplantation.