The macrophage plays an important role in both the innate and acquired (humoral and cellular) immune responses. Their specialized derivatives, the dendritic cells (DCs), are uniquely potent in induction of naive T and B lymphocytes, whereas macrophages influence a range of immune responses by antigen recognition, capture, clearance and transport. They recruit haemopoietic cells to local sites of inflammation and immunity and regulate their activities. We have used various myeloid-restricted membrane antigens and receptors as markers and functional contributors to these activities, and briefly review their role in immune regulation in vivo and in vitro.