Carcinoma of breast is a common disease that kills more number of women worldwide. Asensitive and specific serum marker would be of great help in early diagnosis of malignancy as well as in monitoring the response of cancer patients to therapy. The alterations in the serum level of 3 tumour markers namely, CEA, CA 125 and CA 15-3 at various stages of the disease were investigated in breast cancer patients of Tamil Nadu using Chemi Luminescence Immuno Assay (CLIA) method. The diagnostic significance of the markers were also analysed in three stages of disease namely, non-metastatic, metastatic and post-treatment levels. The results indicated increased levels of all the 3 tumour markers in breast cancer patients. Furthermore, marked elevation was found in patients with metastatic breast disease. Significant reduction was also observed in the post treatment level of CA 15.3. The findings suggest that among the 3 markers analysed, CA 15.3 is indeed helpful for early diagnosis and for predicting the disease response to therapy in breast cancer patients.