The research presented in this thesis describes the production and applications of polyclonal and monoclonal antibodies to warfarin, an anticoagulant used in the management of a variety of thromboembolic disorders. 4'-nitrowarfarin was initially reduced in the presence of zinc and dilute acetic acid to 4'- aminowarfarin, which was characterised by a combination of infra-red spectral and nuclear magnetic resonance studies. 4'-aminowarfarin was then used for the production of a variety of drug-protein conjugates, incorporating different carrier molecules and coupling chemistries. They were subsequently characterised by a combination of SDS-PAGE, UV-spectral studies and size-exclusion high performance liquid chromatography (HPLC) with UV (280 nm) and photodiode array (200-400 nm) detection. The drug-protein conjugates were then used for the production, purification and characterisation of both mouse monoclonal and rabbit polyclonal antibodies to warfarin. Rabbit polyclonal antibodies were initially produced and used in the development of a competitive ELISA for warfarin and also for the development of a BIACORE-based inhibition immunoassay. A panel of murine monoclonal antibodies to warfarin was also generated by somatic cell fusion procedures, using the spleens of mice, following in vivo immunisation with a variety of warfarin-protein conjugates. Positive clones were selected and cloned by limiting dilution. Antibody concentration determinations of purified antibody fractions and ‘spent’ hybridomas were made using a well-based ELISA technique and a biosensor assay. Affinity determinations of the selected monoclonal antibody preparations to warfarin and structurally related analogues were then determined using a well-based ELISA technique and also using several different assay formats using ‘real-time’ biomolecular interaction analysis. The affinity-purified antibody preparations were then used in the development of a BIACOREbased inhibition immunoassay for warfarin in biological matrices. The stability of various immobilised ligands was initially determined and working concentration ranges were determined for each antibody preparation. A selected monoclonal antibody (i.e. 3-2-19) was then used for the determination of warfarin in plasma ultrafiltrate, which reflects the free active concentration of the drug in plasma. The samples assayed by BIACORE inhibition immunoassay were also analysed by HPLC for the purposes of validating the developed immunoassay technique. The technique was then used for the determination of the degree of protein-binding of warfarin in patient plasma samples, following determination of the total warfarin plasma concentration by HPLC.