A bispecific monoclonal antibody (bs-MAb) (OC/TR) was produced in large quantities for the intraperitoneal (i.p.) treatment of ovarian cancer. The bs-MAb recognizes the folate-binding protein on ovarian cancer cells on the one hand and the CD3 activation site on T lymphocytes on the other. T lymphocytes were expanded ex vivo, targeted with OC/TR in vitro and administered to the i.p. cavity in the presence of soluble OC/TR. All patients developed human anti-mouse-antibodies (HAMA). In the Dutch study, 2 complete remissions (CR) were seen, 2 partial regressions (PR), I stable disease (SD) and I progressive disease (PD). In the Italian study 3 CR, I PR, I SD and 2 PD were seen.