The clinical success of pancreas transplantation is limited by the difficulty in diagnosing rejection. In simultaneous pancreas kidney (SPK) transplantation, the diagnosis of pancreatic rejection is particularly difficult in the absence of clinical evidence of kidney rejection. Moreover, patients receiving only pancreas grafts will not have a concomitantly grafted kidney to serve as a "sentinel" for rejection. Percutaneous pancreas graft biopsy has been reported in a few small series but has not been adopted for broad clinical use. We describe the evaluation of 69 consecutive episodes of suspected isolated pancreas allograft rejection by percutaneous pancreas allograft biopsy. These rejection episodes occurred in 41 patients with bladder-drained pancreas transplants (25 SPK, 14 pancrease after kidney transplants [PAK], amd two pancreas transplant alone [PTA]). The indications for percutaneous pancreas biopsy were a twofold or greater increase in serum amylase or lipase, or a sustained 40% to 50% drop in urine amylase in the setting of no evidence of renal allograft dysfunction in SPK transplants. Biopsies were performed with color-flow Doppler ultrasound localization using an 18-gauge automated biopsy needle. Pancreatic tissue adequate for histologic evaluation was obtained in 61 of 69 cases (88%). There were two cases of intraabdominal bleeding, one of which required surgical intervention; the other resolved spontaneously. Histologic assessment of the biopsies demonstrated varying degrees of acute cellular rejection in 48 of 61 specimens (79%). Twelve specimens (20%) were free of histologic evidence of rejection, and one specimen (2%) showed acute pancreatitis. At the time of suspected rejection mean serum amylase and lipase values were increased 3.6 and 8.3-fold, respectively, and urine amylase was decreased by a mean of 45%. We conclude that the commonly used markers for pancreas allograft rejection are only about 80% specific for acute rejection. Percutaneous pancreas allograft biopsy is safe and allows the avoidance of unnecessary antirejection therapy with its attendant side effects and cost.