The effects of insulin and somatostatin on the growth and the colony formation of two human pancreatic cancer cell lines, BxPC-3 and SOJ-6, were studied. The BxPC-3 cell line (American Type Culture Collection no. CRL 1687) was derived from a moderately differentiated pancreatic adenocarcinoma. The SOJ-6 cell line is a subclone of SOJ that was initiated from ascites of a well-differentiated pancreatic adenocarcinoma. Both cell lines express fetoacinar pancreatic antigen, an antigen that might be associated with early transformation stages. However, these lines have different proliferation and tumoral powers. SOJ-6 cells showed an almost twofold higher division rate over BxPC-3 cells when cultured in RPMI-1640 medium containing 10% fetal bovine serum. The tumorigenic degree of SOJ-6 cells, as assessed by tumor growth in nude mice, was about three times greater than that of BxPC-3. The in vitro growth of BxPC-3 cells was significantly promoted by insulin, and was slightly inhibited by somatostatin, whereas the growth of SOJ-6 cells was not influenced by these hormones. Using a clonogenic assay in soft agar, the average ratio of colony numbers formed by SOJ-6 and BxPC-3 was about 10/1, indicating a good correlation between the colony formation and tumorigenic degree in vivo. In this test, the number of colonies formed by BxPC-3 cells was increased about twofold in insulin-supplemented medium. On the other hand, somatostatin inhibited the colony formation by a factor of four to six. However, no hormonal modulation of the colony formation of SOJ-6 cells was observed. Our data show that pancreatic cancer cell lines respond differently to pancreatic hormones, and suggest that this may be correlated to a tumour stage or a tumour type.