Seven patients on dialysis with renal failure received transplants from mismatched cadaver donors and were treated with cyclosporin A (CyA), initially as the sole immunosuppressive agent. CyA was effective in inhibiting rejection but there was clear evidence of both nephrotoxicity and hepatotoxicity. A cyclophosphamide analogue was added to the CyA treatment in six of the patients. Five patients are out of hospital with functioning allografts, and two of these have received no steroids. One patient required an allograft nephrectomy because of pyelonephritis in the graft. Another died of systemic aspergillus and candida infection. Further careful study of this potentially valuable drug will by required before it can be recommended in clinical practice.