On the basis of 26 combined pancreas-kidney transplants we questioned whether both organs undergo rejection simultaneously. Reliable diagnosis of pancreas-graft rejection was made possible by monitoring exocrine graft function, including quantitative measurements of pancreatic juice, its amylase content, and pancreatic juice cytology. In addition, diagnosis of pancreas rejection was based on regular flow studies, daily urinary neopterin excretion, and a retrospective analysis of the clinical course. Clinical symptoms, blood chemistry, and, primarily, histology were used to assess rejection of the kidney allograft. In 18 cases the kidney and pancreas were rejected together; in 8 cases the kidney or the pancreas was rejected. Although both organs were rejected at the same time in most cases, either organ can be rejected alone. Thus, the kidney cannot be used to monitor the pancreas allograft in every case.