AbstractIn this paper we describe the bone marrow‐derived macrophage cell line B6MP102. We describe growth characteristics, responsiveness to biological response modifiers known to activate macrophages (MPs), and the ability of B6MP102—comparable to that of peritoneal MPs—to kill and discriminate tumor cells. We demonstrate that B6MP102 is easily maintained in culture in the presence of 15% L‐M cell‐conditioned media. We have found that the B6MP102 cell line is similar to in vivo‐derived peritoneal MPs. These cells are responsive to biological response modifiers but are not spontaneously cytotoxic. They produce O−2in quantities comparable to that produced by peritoneal MPs, and they exhibit target ranges for direct killing similar to those of activated peritoneal MPs. In addition, B6MP102 is similar to MPs in mediating cytostasis. These latter two points are especially significant, suggesting that the mechanisms that MPs may use to distinguish and kill tumor cells are retained in the B6MP102 cell line. This makes the cell line a useful tool for studying MP‐tumor cell interactions.