Serum levels of CEA, CA 15.3 and CA 27.29 were measured during the follow-up of 499 breast cancer patients. Studies included three different groups of women: 82 blood donors free of disease, 42 patients with non-malignant breast diseases and 499 breast cancer patients. After the determination of cut-off values, serum levels of tumor markers did not show significant elevations in benign breast diseases. On the basis of our results CA 15.3 (sensitivity = 57%; accuracy = 87%) was the most effective marker, CA 27.29 (sensitivity = 62%; accuracy = 83%) was the most sensitive and CEA (sensitivity = 45%; accuracy = 81%) was the least sensitive and effective marker. The combined use of markers was evaluated by step-wise logistic regression analysis. The regression coefficients showed that CA 15.3 (coeff. = 2.97) and CA 27.29 (coeff. = 1.46) were suitable for the detection of possible metastases during follow-up. Finally, we studied the relationship between pT, pN, pM and circulating levels of CA 15.3 and CA 27.29.