The pathogenetic mechanism underlying glucose intolerance in pancreatic cancer is still unclear. We studied the pattern of three glucose regulating hormones (C-peptide, glucagon and GH) in pancreatic cancer patients with (N = 34) and without (N = 8) hyperglycemia, and compared the findings made with those from subjects with other hyperglycemic conditions of well-known origin [type I diabetes mellitus (8 cases) and diabetes mellitus secondary to chronic pancreatitis (13 cases) or liver cirrhosis (4 cases)]. In hyperglycemic pancreatic cancer patients, C-peptide was absent in 26% of the cases, reduced in 24%, elevated in 29% and within the normal range in the remaining 21%. In normoglycemic pancreatic cancer this hormone was reduced in two cases (25%) and within the normal range in all the others. GH was within the normal range in all cases: glucagon was below the normal range in some hyperglycemic pancreatic cancer patients (41%) or within the normal range in all the remaining patients. No correlations were found between the three hormones when findings from subjects were considered all together. However, in pancreatic cancer C-peptide and glucagon presented consensual variations. C-peptide, glucagon and GH levels were not related to tumor volume; glucagon was found to be associated with liver metastases. C-peptide was correlated with serum ALT and ALP. We may conclude that hyperglycemia associated with pancreatic cancer may be caused by different mechanisms. In some cases a reduced secretion of both insulin and glucagon was observed, as occurs in chronic pancreatitis. In the majority of patients, beta cell function appears normal, and the hyperglycemic state may depend on an altered peripheral sensitivity to insulin due to the pancreatic pathology itself or to consensual liver involvement.