Human mammaglobin (hMAM) mRNA is considered to be a promising candidate for a sensitive molecular marker for breast cancer. In this study, we attempted to relate the presence of hMAM mRNA in the peripheral blood with certain established clinicopathological features of breast cancer in order to validate its clinical utility. A total of 139 subjects including 79 with localized cancer, 33 with metastatic disease, and a control group of 27 individuals were studied. hMAM mRNA expression was assessed by reverse transcriptase polymerase chain reaction on cells from peripheral blood. The expression of hMAM mRNA was found in 0 of the 27 control subjects, 1 of the 8 stage 0 (12.5%) patients, 4 of the 16 stage I (25%) patients, 13 of the 40 stage II (32.5%) patients, 5 of the 15 stage III (33.3%) patients, and 18 of the 33 (54%) cases of metastatic disease. There was a statistically significant (P=0.045) difference in frequency between patients with localized disease (29%) and those with metastatic disease. Although trends of increasing frequency of hMAM mRNA expression existed in patients with unfavorable prognostic factors, including primary tumor size, T stage, N stage, overall stage, presence of angiolymphatic permeation, negative estrogen receptor, high 5-phase fraction (>7%), and aneuploid DNA index, none of the differences was significant. In conclusion, the clinical utility of hMAM mRNA may not be in screening or staging of breast cancer, but in following patients after surgery to detect recurrence. Further evaluation of hMAM mRNA in combination with other molecular markers to follow post-operative breast cancer patient is warranted.