Breast cancer is the most common female malignancy affecting approximately one woman in eight. Many attempts have been made to define markers which may have potential clinical applications in diagnosis as well as therapy. New isoforms of CD44 with alternative spliced exons have recently been described. We studied the expression of CD44 exon 6 using a semi-quantitative RT-PCR reaction on a panel of 25 normal breast specimens, 10 mammary fibroadenomas, eight cystic samples and 52 primary breast tumors. Significant correlation was found between CD44 exon 6 expression and the overall survival of the N-M-population, P = 0.032, (logrank test by Mantel's method). The same result was also observed for the disease-free survival, P = 0.000002 (logrank test by Mantel's method). CD44 exon 6 expression, as detected by our RT-PCR-based method, might be a useful prognostic indicator of metastasis in breast cancer. However, these preliminary results need to be confirmed by later retrospective and prospective studies on a larger number of patients.