In a group of breast cancer patients post-operatively followed-up by serum CEA, TPA, and CA15-3 level determinations, the CA549, CA M26 and CA M29 values as well were measured. In metastatic patients, CA549 and CA M26 showed a sensitivity only slightly lower (70% and 67%, respectively) than that of TPA which was the highest (78%), while CA M29 sensitivity (58%) was much lower than that of TPA and similar to CEA (57%). In non-relapsed patients, CA M26 and CA M29 showed a specificity (95% and 92% respectively) similar to CEA (86%) and CA15-3 (92%) and much higher than TPA (73%). Among the possible associations of all the studied tumor markers, the CA M26-CA M29-CEA one seems the most promising because of its high sensitivity and specificity. Benign liver diseases and/or diabetes are probably the reasons most often responsible for the aspecific increase in serum CA549 values. On the other hand, they seem to affect the CA M29 much less and the CA M26 almost not at all.