We report on a 22-year old patient who received a cadaveric renal transplant following haemodialysis treatment for five months due to endstage chronic glomerulonephritis. 14 months after successful transplantation while on stable renal function (serum-creatinine 1.0-1.4 mg%) the patient became pregnant. As an immunosuppressive therapy the patient got cyclosporine A and cortisone. The monitoring of the immunosuppressive therapy (Cyclosporine A) was performed by daily measurement of serum concentration by radioimmunoassay. Drug administration was adjusted to maintain serum levels of 250-550 ng/ml. Increased dosages were required from 25th week until delivery. Until the 25th week of gestation the pregnancy was uncomplicated from both the nephrological and obstetrical points of view. At the 25th week of gestation the patient became anuric. This was caused by a postrenal failure due to the compression of the transplantar ureter by the pregnant uterus. Nephrostomy was installed and was used until the end of pregnancy. In the third trimester the foetus showed growth retardation. For this reason a Caesarean section was necessary at the 36th week of gestation. A healthy boy was delivered weighing 2080 g and measuring 45 cm. No congenital malformations were observed, the chromosomal analysis showed no aberrations. After the delivery cyclosporine concentrations in the blood of the mother and the newborn were simultaneously measured. A remarkable difference in these concentrations was observed particularly in the mother's blood 864 ng/ml whereas in the baby's blood the concentration was 312 ng/ml. Three days after the delivery the patient was able to urinate normally so that the nephrostomy could be removed.