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The aim of the study was to assess the ellipsometry analytical complex for its diagnostic potential related to colorectal cancer and metastases of different localization. The proposed ellipsometry was aimed to complement the current non-invasive optical methods based on the reflection of polarized light near the surface plasmon resonance under full internal reflection. Materials and Methods. We measured the highly specific and sensitive reaction between tumor-associated M2-pyruvate kinase and the respective monoclonal antibodies immobilized on chips. The biological material (blood serum) was obtained from healthy (cancer-free) subjects (n=19) and from patients with colorectal cancer of various localizations (n=49). The examined patients were divided into three subgroups depending on localization of the metastases: 1 st subgroup-local-regional colorectal cancer (n=15); 2 nd subgroup-hepatic metastases only (n=18); 3 rd subgroup-extrahepatic metastases (n=16). We also determined the concentrations of tumor M2-pyruvate kinase during its interaction with the monoclonal antibodies. In this, we measured the refractive index of the chip near-surface area by using highly sensitive optical systems able to measure the light polarization near the surface plasmon resonance. Results. The interaction of serum M2-pyruvate kinase with the antibodies leads to a noticeable change in the optical properties of the medium, which indicates a high specificity of this reaction. We found significant differences (>20-fold) in the equilibrium levels of serum M2-pyruvate kinase both in healthy individuals and in patients with colorectal cancer, as well as in patients with metastases of various localizations. The diagnostic potential of these optical methods in respect to cancer-specific serum M2-pyruvate kinase as a marker of colorectal cancer was confirmed by subsequent ROC analysis. Conclusion. The results obtained are promising for the development of methods for early diagnosis of colorectal cancer, for the detection of metastases of various locations, and (in the long term) for the detection of the recurrent disease, as well as for the treatment follow-up.