The biochemical mechanisms underlying the processes of chemotaxis, adhesion, phagocytosis and lysosomal enzyme secretion are described. Particular attention is drawn to the roles of aerobic glycolysis, the hexose monophosphate shunt, cyclic adenosine monophosphate, cyclic guanosine monophosphate and the microtubular and microfilament systems. The way in which drugs modify these pathways is discussed with reference to agonists and antagonists of beta-receptors, agonist and antagonists of muscarinic receptors, prostaglandins, colchicine, Cytochalasin B, and to steroidal and non-steroidal anti-inflammatory agents. The possibility that anti-inflammatory agents produce a significant effect in this manner is considered.