Eighteen patients with measurable or evaluable advanced (metastatic or unresectable) adenocarcinoma of the pancreas were treated with a single infusion of monoclonal antibody CO17-1A in autologous leukocytes. No toxicity was experienced with treatment. Three of seventeen patients evaluable for response demonstrated unusually stable disease and a decrease in serum CA 19-9 antigen in two patients who expressed this biomarker. Human anti-mouse antibody developed in 81% of these patients. Monoclonal antibody CO17-1A may have a cytostatic effect in a small fraction of patients. Future clinical trials will focus on enhancing this effect with other immune modulators.