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Two murine Mabs VA1(IgG1) and VA2(IgG1) were produced against a bacterial fusion protein comprising glutathione S-transferase and five tandem repeats of the MUC1 protein. Using the immunoperoxidase staining technique, VA1 detected 46/53 and VA2 detected 48/53 breast cancers and both also reacted with a range of other human epithelial carcinomas. In addition VA1 gave weak reactions with normal breast tissues whereas VA2 was non-reactive and could be a relatively tumour specific antibody for breast cancer. The antibodies were also tested by ELISA-VA1 reacted weakly with glycosylated HMFG but strongly with deglycosylated HMFG, whereas VA2 reacted strongly with both forms of HMFG. The reactivities of the two Mabs with synthetic peptides of the MUC1 tandem repeat were used to map the epitopes recognised by VA1 (amino acids RPAPGS) and VA2 (amino acids DTRPA). The use of fusion proteins provides another means of immunisation to produce anti-tumour antibodies.