Results of Cyclosporin A (CyA) treatment following kidney transplantation in 16 children are reported. CyA was used in combination with low-dose prednisolone. The dosage of CyA was related to body surface area, starting with 500 mg/m2 daily and was reduced weekly by 50 mg/m2 until the maintenance dose of 300 mg/m2 was reached at the end of the fifth week. The dosage was controlled and adjusted by monitoring the CyA blood concentrations. In comparison with adults, children required higher CyA doses related to body weight to maintain the desired trough blood level range (200-750 ng/ml). In 16 children treated with CyA the graft function rate at three months was 100% and at six months 90%, because one patient died of septicemia. 10 patients experienced 20 reversible rejection episodes. Infectious complications and side-effects were similar to those observed in adults. Almost half of the patients exhibited transient nephrotoxicity which reversed after dose reduction. It is concluded that CyA treatment in a body surface area related dosage and in combination with blood level monitoring offers a successful way for kidney transplantation in childhood.