The combination of the different chemical mediators likely to promote pain is often at the root of disturbances affecting both microcirculation and capillary permeability, as several studies have shown. These same disturbances are to be encountered in different types of illnesses in which pain dominates the clinical picture. Recent theoretical and experimental studies have also suggested that haemodilution might have beneficial effects on these rheological disorders. Three clinical observations (arteritis of the lower limbs, persistent post-phlebitic ulcer, myocardiac ischemia) demonstrate the therapeutic benefits of this technique, particularly regarding pain.