One major problem in primary breast cancer is the identification of new parameters able to select patients at high risk of recurrence. Our study was aimed at detecting mammary tumor cells in the bone marrow of breast cancer patients using a single bone marrow sampling and the monoclonal antibody AB/3. This antibody recognizes a membrane carbohydrate epitope present in human breast cancer cells but not in normal tissues. Only 2 out of 45 breast cancer patients were found to have a bone marrow positive AB/3 staining reaction. Our data confirm and extend previous reports that single bone marrow sampling coupled with immunocytochemistry is not sensitive enough to be used as a routine procedure to acquire prognostic information in breast cancer.