Human mammaglobin (hMAM) has recently been recognized as a breast associated glycoprotein. Although the biological role of hMAM is unknown, it has been previously reported that hMAM gene expression is a marker of low biological and clinical aggressiveness of breast cancer (BC). In this study, 148 cases of BC tissues were investigated for hMAM mRNA expression by reverse transcriptase-polymerase chain reaction (RT-PCR). In order to evaluate its prognostic value, hMAM was correlated with age of patients, type and size of tumor, nodal stage, histologic grade, c-erbB-2 over expression, Ki67 labelling index, estrogen receptor (ER) status and progesterone receptor (PGR) status. Fisher's exact test was used to examine the association between different parameters and hMAM. hMAM was expressed in 138/148 (93%) of BC tissues examined. Among the 10 hMAM negative cases, 8 were invasive ductal carcinomas (microscopically higher G3 grade) and 2 infiltrating lobular carcinomas. We found a significant association (p = 0.020) between absence of hMAM mRNA and G3 histologic grade but not with any other prognostic parameters studied. The present study indicates that lack of hMAM expression is restricted to the BC with G3 grading. Further studies are needed to clarify the biological basis and the clinical significance of our results.