Blood viscosity is an important cardiovascular risk factor that might be related to diabetes complications. Hyperinsulinemia has been suggested as "the most important candidate" to characterise diabetes as a risk factor for cardiovascular disease. There is no evidence of the beneficial effect of insulin on type 2 diabetes erythrocytes in patients without cardiovascular disease, whereas the opposite is observed in those with cardiovascular disease. In the present study we analysed the in vitro effect of different doses of insulin on red blood cell rheological aspects in an obesity model. Previous studies carried out in beta strain rats had shown that this strain possess insulin blood levels higher than the ones observed in alpha strain (eumetabolic), as well as blood hyperviscosity and erythrocyte deformability decrease. Our results points out that in vitro insulin produced an increase in erythrocyte aggregability, although it did not modified either their osmotic fragility or erythrocyte deformability estimated by viscometry, even against decreased viscosity of treated erythrocytes submitted to increased shear rate.