Blood and plasma viscosities were determined using respectively a Couette type micro-viscometer (LS 30) and an automatic capillary viscometer (FICA). Plasma beta-thromboglobulin (beta-TG) levels were determined by radioimmunoassay. These parameters were measured in a group of 11 poorly controlled insulin requiring diabetics before and after blood glucose normalization using an artificial pancreas (Biostator GCIIS). Before connection to the artificial pancreas, blood and plasma viscosity and beta-TG levels were significantly higher in diabetics than in controls. The strict metabolic control obtained by the artificial pancreas resulted in a normalization of the hemorheological parameters and in a significant reduction of plasma beta-TG levels after 48 h. These results suggest that the metabolic control of diabetes influences the rheological behavior of blood and the metabolism of platelets.