A member of the human minichromosome maintenance complex protein family, hCDC47 (alias MCM7) has been identified as a component of the regulatory mechanism in cell proliferation. The expression of this protein, as determined by immunohistochemistry, was investigated to determine its application as a proliferation marker. A mouse monoclonal antibody (Clone 47DC141, NeoMarkers, Fremont CA) raised against recombinant hCDC47 protein was tested against a wide range of tissues. Immunoreaction patterns were determined in normal and neoplastic, human tissues, including skin, tonsils and lymph nodes, primary, and metastatic brain tumors. The protein was detected in the nuclei of both, normal and neoplastic proliferating cells. Similarly, we also examined the distribution of hCDC47 in normal rat and mouse tissues, and rodent and human tumors grown in nude mice.The pattern of immunolocalization was identical to that seen in human tissue, with positive nuclear immunoreaction readily identified in proliferating cells. Western immunoblot was carried out on extracts from PANC cells (human pancreatic adenocarcinoma cell line) to confirm the specificity of the protein. To correlate Ki67 protein immunoexpression with hCDC47 antibody reactivity, semiquantitative comparisons were carried out on parallel tissue sections. There was excellent correlation in the distribution pattern of the 2 markers, although hCDC47 was more sensitive.Thus this marker may have important clinical and research applications because of its activity in formalin-fixed, paraffin-embedded, proliferating, normal, and neoplastic tissue. More significantly, its application to animal tissue makes it a reliable and easy to use, proliferation marker for experimental studies.