The trifunctional antibody catumaxomab with bispecificity for the epithelial cell adhesion molecule EpCAM and the T-cell antigen CD3, is a new therapeutic strategy for ovarian cancer patients with symptomatic malignant ascites. Whether or not intraperitoneal (i.p.) catumaxomab-therapy has influence on disseminated and circulating tumor cells was investigated by analyzing cytokeratin-positive (CK+) cells in bone marrow (BM) and peripheral blood (PB). Fourteen ovarian cancer patients with symptomatic ascites were treated with catumaxomab (up to 5 i.p.-infusions; increasing dosages (10-200 microg)). CK+-cells were isolated before and after antibody-therapy by density gradient centrifugation and immunocytochemistry (anti-CK antibody A45-B/B3). Catumaxomab-treatment resulted in the sustained reduction of ascites flow and arrested ascites reaccumulation. The mean overall survival was 8 months. CK+-cells in the BM were found in 70% before and 83% after therapy (in the PB 57% and 42%, respectively). A marked reduction of CK+-cells occurred in the BM in 2 and in the PB in 4 patients. Catumaxomab shows a strong intraperitoneal effect and possibly also systemic effects on tumor cells in the BM and PB.