A recombinant Fv (variable fragment) has been produced for the murine monoclonal antibody HMFG1. This antibody was raised against human milk fat globules and reacts with an epitope (PDTR) in the protein core of MUC1 mucins, which are up-regulated in human breast and other carcinomas. Binding specificity of the Fv fragment has been demonstrated through immunoaffinity purification, and by radioimmunoassay. The affinity constants for this Fv fragment and for the proteolytically produced Fab (antigen binding fragment) of the related humanised antibody HuHMFG1 were determined by monitoring the fluorescence quenching of the antibody fragments whilst adding aliquots of MUC1 related antigenic peptides KAPDTRPAPG and VTSAPDTRPAPG. Using these techniques it has been demonstrated that the products of these different methods of antibody fragmentation are comparable, and suitable for solution structure analysis using nuclear magnetic resonance (NMR) spectroscopy.