CCK-secreting WE rat medullary thyroid carcinoma cell line resembles other calcitonin-producing (C-cell) lines in that calcium, cAMP, or agents which raise cAMP, dexamethasone, and beta-adrenergic agents all stimulate peptide secretion. Unlike other C-cell lines, the WE cells respond similarly to IBMX (3-isobutyl-1-methyl-xanthine, a phosphodiesterase inhibitor) in the presence and absence of forskolin, implying that these cells secrete substances that raise cAMP levels, whose effect is accentuated by IBMX. Both CGRP and neurotensin, peptides that may be secreted by these cells, caused a small, but significant, increase in CCK secretion. It is possible that these or other secreted substances that activate adenylate cyclase are responsible for the cell's high rate of CCK secretion. Their high rate of CCK synthesis and their regulated secretion suggest that these cells will be a good model for studies of CCK expression, biosynthesis, and processing.