Since 1985, 150 patients with pancreatic ductal adenocarcinoma have been treated with the monoclonal antibody BW 494 in four different multicentric trials in Germany. The antibody recognizes a human pancreatic cancer associated antigen and mediates an antibody dependent cellular cytotoxicity (ADCC) in vitro, when human mononuclear cells are coincubated as effector cells. In patients with at advanced unresectable pancreatic cancer there where two phase-I-studies finished in 1987 and 1989, respectively, and one uncontrolled phase-II-study finished in 1988. In 1987, we started a controlled randomized trial in patients with resectable (Whipple) pancreatic cancer, which will be finished in 1990. There were no major side effects if the intravenous antibody application was restricted to a 10-d treatment protocol (up to 370 mg given in 10 different dosages). Human anti-mouse-antibodies could be demonstrated in all patients investigated for within 4 wk after immunotherapy. In patients with advanced pancreatic cancer (n = 87), monoclonal antibody treatment did not induce significant response rates. There was stable disease in 1/3 to 1/2 of the patients lasting three months or longer. Therapeutic success may be expected in patients with minor tumor burden.