To date one of the major dilemmas in clinical pancreas transplantation is the lack of a reliable indicator for pancreas rejection. In a consecutive series of 52 patients undergoing simultaneous pancreas and kidney (SPK) transplantation with bladder drainage technique between October 1991 and December 1992 a new test using serial levels of serum human anodal trypsinogen (HAT) was evaluated for its efficacy to detect pancreas rejection. Postoperative baseline levels of HAT were compared to peak HAT values at time of rejection. HAT profiles at time of rejection were calculated and compared to profiles of urinary amylase, serum amylase, fasting blood sugar and serum creatinine. In this series one year patient survival was 97%, graft survival of the pancreas 86% and of the kidney 90%. In 71% of the patients at least one rejection episode occurred. At time of kidney-biopsy proven rejection with a concurrent serum creatinine rise a significant HAT level rise to more than 1000 ng/ml was observed from baseline levels of 200 ng/ml (P < 0.001) indicating kidney and pancreas rejection (73%). Urinary amylase levels decreased in the majority of rejection episodes at the same time from baseline levels to less than 20,000 U/l. In 25% of the rejection episodes a significant serum creatinine rise was observed without a HAT rise or urinary amylase decrease indicating kidney-only rejection, while in 2% a urinary amylase decrease and simultaneous HAT also was observed with a negative kidney biopsy indicating pancreas-only rejection. We feel that increase in HAT levels significantly correlates with pancreas rejection. After SPK, determination of HAT is an additional helpful non-invasive test. In pancreas transplantation alone HAT can be a useful indicator to detect rejection and facilitate timing of a pancreas biopsy and initiation of antirejection treatment.