The normal role that the macrophage plays in tissue homeostasis is presented along with the morphological and functional changes that occur to the macrophage population as the lymphoedema progresses from the latent to the chronic phase and then with the treatment with a representative benzopyrone called coumarin. Underlying the lymphoedema, there is a chronic inflammation. It is this, in association with the accumulating protein and the subsequent alterations it produces in the tissues that attract monocytes and macrophages to the affected area. Despite the fact that macrophages are facultative anerobes, and that larger numbers than normal accumulate, the tissue conditions result in a depression in their activity levels. Apart from these tissue conditions there is the possible production of deactivating proteins such as transforming growth factor beta 1 and 2. Evidence for this deactivation comes from enzymatic studies in which levels of typical macrophage enzymes are reduced and from morphological work which has shown a reduction in pseudopods and a tendency to accumulate large amounts of lipid in their vacuoles.