Twenty-six patients with non-functioning pancreatic endocrine tumor (NFPET) were operated on during a 22-year period (1968-1990) at PUMC Hospital, Beijing. Of these, 19 were female and 7 were male with a mean age of 33 years. All these tumors, including 12 malignant and 14 benign, were solitary, and most of them were well-encapsulated. Immunohistochemical staining showed 23 (88.5%) containing 1-4 kinds of peptide hormone and 18 (69.2%) being multihormonal. In 7 of the 9 tumors subjected to electron microscopic study, various amounts of neurosecretory granules were found. Tumors of this series were clinically silent, but they contained some immunoreactive peptides, although the amount of the peptides varied from tumor to tumor.