Monoclonal antibodies are accepted as ideal adjuvant therapeutic reagents for all kinds of diseases. Polyvalent (cross-linking) and low-mutated IgM antibodies (less immunogenic) are believed to be the most effective weapons against cancer. The best sources for these types of antibodies are the cancer patients themselves. Using conventional hybridoma technology, not only are fully human monoclonal IgM antibodies isolated, but also new tumor-related targets can be identified using the same experimental approach. The resulting antibodies can be used directly for therapeutic purposes without further modulation and manipulation. This report describes five newly established human monoclonal IgM antibodies; antibody LM-1 that was isolated from a patient with lung cancer, antibodies PM-1 und PM-2 that were isolated from a patient with pancreatic cancer, and antibodies CM-1 and CM-2 which were isolated from a patient with colon carcinoma. The mainly germ-line encoded antibodies are specific for malignant tissues and show only restricted reactivity with healthy cells. When tested for in vitro functional activity, all five antibodies inhibit tumor cell proliferation of carcinoma cells by inducing apoptosis.