Urine cytology and blood lymphocyte blastogenesis were evaluated as indicators of allograft rejection in a porcine pancreatic transplantation model. The percentage of activated lymphocytes and/or blasts was significantly increased during the rejection phase. Positive cytology was present in all rejection episodes. An increased thymidine uptake of blood lymphocytes and a decreased uridine/thymidine uptake quotient were seen prior to the onset of rejection. The reported dissociation of anionic and cationic trypsin levels in serum and urine after transplantation was not seen after simple urinary diversion of the pancreatic juice. This supports the hypothesis that a decreased synthesis of cationic trypsinogen compared with anionic trypsinogen occurs after porcine pancreatic transplantation.