The Agricultural Research Center of the United States Department of Agriculture identifies bovine respiratory disease (BRD) as the most common and costly disease of feedlot cattle in the United States (1). The alveolar macrophage serves as the first line of defense for the lung alveolus by recognition, phagocytosis, and destruction of the bacterial agents reaching the alveolus. CD163 is a monocyte/macrophage-restricted, cysteine-rich, scavenger receptor that binds and internalizes circulating haptoglobin-hemoglobin (Hp–Hb) complexes (5). Macrophages expressing high levels of CD163 appear to be present in the resolution phase of inflammation (7). The purpose of this study was to further our understanding of the cellular regulation of host inflammatory mediators in bovine respiratory diseases by determining the expression of CD163 on alveolar macrophages and peripheral blood mononuclear derived macrophages. Bovine peripheral blood mononuclear cells (PBMC) were isolated from the whole blood of healthy calves and cultured for differentiation into macrophages. After cellular differentiation, the cultured cells and freshly isolated alveolar macrophage cells obtained by bronchoalveolar lavage were labeled with anti-CD163 antibodies and evaluated for expression of CD163 by flow cytometry. Positive expression of CD163 (61.83%) was observed on alveolar macrophages. These findings demonstrate that bovine macrophages do express a surface protein similar to CD163. Nevertheless, neither the peripheral blood monocytes nor the monocyte-derived macrophages expressed CD163 in any of our trials. Four of the six flow cytometry runs also did not reveal a high level of monocyte-macrophage differentiation, however, with the modification of our isolation and culturing techniques, the final two flow cytometry runs demonstrated higher levels of cellular differentiation. Additional studies are needed to determine expression of CD163 on macrophages derived from peripheral blood mononuclear cells, and alternative methods of differentiation will be necessary to reproducibly induce CD163 expression and further the understanding of the CD163-associated, anti-inflammatory pathway.