Chromogranin A (CgA) is a neuroendocrine protein that undergoes proteolytic cleavage in secretory granules. The aim of the present study was to characterize the peptides WE14 and EL35 that are derived from evolutionarily conserved regions of CgA in rat and human endocrine tissues. In the rat pituitary, HPLC analysis revealed that WE14 is present as a single immunoreactive peak, whereas EL35 elutes in two molecular forms. Authentic WE14 is also produced in both rat and human adrenal glands, while EL35 displays a variable elution profile depending on the tissue extract, indicating the existence of different forms of EL35 in these tissues. Immunohistochemical labeling of the rat pituitary showed that WE14 and EL35 occur in gonadotropes and melanotropes, but not in corticotropes. A strong immunoreaction for both peptides was also observed in rat adrenochromaffin cells. In the human adrenal gland, the WE14 and EL35 antisera revealed intense labeling of adrenomedullary cells in adult and nests of chromaffin progenitor cells in fetal adrenal. Finally, WE14 and EL35 immunoreactivity was detected in pheochromocytoma tissue where WE14 occurred as a single immunoreactive form, while EL35 displayed different forms. The observations that WE14 and EL35: (1). have been preserved during vertebrate evolution, (2). are processed in a cell-specific manner, and (3). occur during ontogenesis of the adrenal gland strongly suggest that these peptides play a role in endocrine tissues. In addition, the existence of differentially processed CgA-derived peptides in normal and tumorous tissues may provide new tools for the diagnosis and prognosis of neuroendocrine tumors.