Pronounced and direct relations exist between hemorheologic blood disease and microcirculation in disorders of red blood cells. Within this framework, sickle cell anemia appears as the typical hemorheologic disease clearly illustrating the hemorheology-microcirculation-thrombosis relation. In acquired diseases, particularly those vascular disorders most concerned, the relation is indirect: the hemorheologic disorder predisposes to plasma and cell occlusion of the vascular lumen, probably labile and pre-thrombotic but influencing microcirculation blood flow. The role of endothelial cells and vascular wall in the appearance and localization of this phenomenon is unknown at present. Pharmacologic interest is considerable in both cases, with emphasis on the use of drugs of both cellular but also intercellular and parietal activity.