The human monoclonal antibody SC-1 was isolated from a patient with a diffuse-type adenocarcinoma of the stomach and induces apoptosis of stomach carcinoma cells by binding a stomach-carcinoma-associated isoform of CD55/DAF-B. In a first clinical trial with 20 patients with poorly differentiated stomach adenocarcinoma of diffuse-type received 20 and 30 mg of purified SC-1 antibody intravenously, followed 24 or 48 h later by gastrectomy and lymphadenectomy. In 90% of the cases a significant induction of apoptotic activity was measured in primary tumors as compared with earlier biopsy material and in 50% of the patients a significant regression of tumor mass could even be determined histopathologically. No toxic crossreactivity was observed with normal tissue or organs of patients. These data show, that the human monoclonal antibody SC-1, which induces tumorspecific apoptosis, can be successfully used for adjuvant therapy.