Monocyte chemotactic protein-1 (MCP-1) is a chemokine involved in the macrophage infiltration of tumor tissue. Tumor associated macrophages (TAMs) are a population of mononuclear-phagocytic cells, which can express complex functions related to tumor biology. The present study was designed to analyse the expression of MCP-1 in parenchymal and stromal elements on frozen sections of 27 breast invasive ductal carcinomas not otherwise specified (NOS) by immunohistochemistry. The expression of MCP-1 in tumor parenchyma and the degree of tumor differentiation were assessed. MCP-1 was detected in the parenchyma in 15 of 27 ductal carcinomas. Positive immunoreactivity manifested as diffuse, homogeneous, moderate or strong, cytoplasmic staining, confined to tumor epithelium. Generally, MCP-1-negative tumors tended to be well differentiated, while chemokine-positive tumors exhibited a low level of differentiation. MCP-1 immunoreactivity was also present in TAMs (CD68 positive cells) in 23 of 27 tumors, and in endothelial cells in 11 of 27 tumors. These results indicate that parenchymal and, more variably, stromal elements of human invasive ductal carcinomas NOS can express MCP-1 in vivo. Additionally, these findings suggest that MCP-1 expression in tumor parenchyma is correlated with the histological grade of ductal invasive breast carcinoma.