The object of this study was to examine whether MUC-1 can be detected in the axillary lymphatic drainage of patients who have undergone conservative surgery for breast cancer and to assess the correlations between the presence of MUC-1 and prognostic factors in breast cancer. Sixty-eight women with invasive ductal carcinoma of the breast underwent wide local excision and axillary lymph node dissection. Axillary drains were inserted in all these cases, and the presence of MUC-1 and beta-actin was evaluated by RT-PCR in the lymphatic fluid collected after the operation. Prognostic factors included tumour size and grade, vascular and lymphatic invasion, clearance margins of the resected specimens and status of the axillary lymph nodes. RT-PCR assays for MUC-1 in the axillary fluid were positive in 17 patients (25%). The presence of MUC-1 was associated with increased tumour size and showed a positive correlation with axillary lymph node metastases and incomplete resection of the tumour. RT-PCR can disclose cancer cells in the axillary fluid after conservative surgery for breast cancer. The presence of MUC-1 in the axillary drainage may be associated with poor prognostic features, and its detection may have implications for therapy as it suggests that re-excision should be considered.