This thesis assesses the potential use of PrP^c as a surrogate marker for CJD by an analysis of blood from vCJD patients, sCJD patients, non-CJD neurological controls and healthy adults. PrP^c was measured by DELFIA and cell-associated PrP was measured by flow cytometry. These are differences in free and cell-associated PrP found in blood of CJD patients and control groups, some of which may be useful as surrogate markers of disease DELFIA analysis identified a significant reduction in the concentration of PrP^c in the whole blood of vCJD and non-CJD neurological patients compared with healthy adults. A significant elevation was found in plasma PrP^c in sCJD patients compared with healthy adults and neurological controls. Flow cytometry found no significant differences between groups in the expression of PrP on platelets and lymphocytes. Neurological controls show significantly less PrP on red cells than healthy adults. In addition the development of a DELFIA based test designed for the detection of the disease-associated PrP^Sc in human peripheral blood is the other main focus of research studies detailed within this thesis. Sensitive assays have been developed using existing techniques allowing the detection of PrP^Sc in the central nervous system and peripheral lymophoreticular tissues of patients with vCJD as validatory studies prior to application of these assays to patient blood samples. Atomic dielectric resonance spectroscopy analysis techniques have also been used to investigate potential differences in frequency and atomic resonance, which may allow identification of characteristics distinct to vCJD peripheral blood samples.