The ability to detect biomarkers in human serum is important for cancer diagnostics. The work presented focuses on the establishment of a surface plasmon resonance (SPR) biosensor as a means for detecting varying levels of autoantibody biomarkers in human serum samples. Carcinoembryonic antigen (CEA) is a biomarker that is present in human serum. It is thought that CEA levels become elevated in patients with colon and ovarian cancer, causing a corresponding increase in the autoantibody level in human serum. Detection of this CEA autoantibody increase could be used to diagnose cancer in patients. Using a SPR biosensor, human serum samples were screened directly for CEA antibody levels. Results using a sandwich assay with a SPR sensor demonstrated the same linear trend as seen from an established enzyme-linked immunosorbent assay (ELISA) method. Serum samples from five healthy individuals were used to establish a threshold value for differentiating a cancerous serum sample from a negative sample with a 95% confidence. Three serum samples from cancer patients with positive CEA antibody levels as evaluated by ELISA were used to test the criterion.