1. Serum amyloid A (SAA) levels were studied in 35 recipients of cadaveric renal transplants. Marked SAA elevations were seen during all acute allograft rejection episodes. The mean peak SAA level in well-documented rejections was 446 mg/l (median 415 mg/l, range 132–1040 mg/l; controls < 1 mg/l).
2. Rejections in patients receiving cyclosporin-A alone as post-transplantation immunosuppressive medication were characterized by a significantly higher peak SAA level than rejections in patients receiving cyclosporin-A in combination with methylprednisolone (539 ± 53 mg/l, mean ± sem, vs 226 ± 9 mg/l, P < 0.01).
3. Excluding surgery-induced SAA elevations in the immediate postoperative period, seven significant SAA peaks not related to allograft rejection were observed. These were associated with surgical complications and infections, and in one case probably with the underlying rheumatic disease, which was complicated by amyloidosis.
4. The results show that acute renal allograft rejection induces a dramatic acute phase SAA response. Since SAA is an easily measured serum component and the rejection-induced elevation is an early event, monitoring of SAA in kidney transplant patients-5-have considerable clinical significance.