The role of T cells, macrophages and platelets in asthma is discussed. Peripheric T cell populations are normal as well in atopic as in non atopic. Macrophages can release histamine releasing factors and PAF in presence of allergens. Platelets stimulated by contact with allergens or PAF decreased the aggregation pattern induced by common inducers. These data show that different cells can play a role in the inflammatory process in asthma.