Acrylamide which is formed via reaction of reducing sugars with amino acids during food processing at high temperatures is not only neurotoxic and carcinogenic, but it also damages erythrocyte membrane and generates micronucleated erythrocytes. In the present study, effects of chronic administration of acrylamide at a dose which does not induce neurotoxicity were evaluated on blood viscosity parameters (hematocrit, erythrocyte deformability, erythrocyte aggregation and plasma viscosity). Twenty adult male Sprague-Dawley rats were divided into control and acrylamide groups. The acrylamide group received 10 mg/kg/day acrylamide, whereas the control group received saline (vehicle), both in 10 ml/kg/day volume via gastric gavage. Erythrocyte aggregation and deformability were measured with LORCA and plasma viscosity with cone-plate viscometer. Erythrocyte deformability was measured before, and at the end of the 3rd and the 5th weeks of acrylamide administration. Hematocrit, erythrocyte aggregation and plasma viscosity were measured only at the end of the 5th week. Acrylamide caused a significant decrease in the deformability index of erythrocytes (at the end of the 3rd week, control: 0.606 +/- 0.003, acrylamide: 0.595 +/- 0.003, p < 0.05) (at the end of the 5th week, control: 0.606 +/- 0.002, acrylamide: 0.588 +/- 0.002, p < 0.01). Aggregation tendency and plasma viscosity were slightly higher in the acrylamide group, however the difference was not statistically significant. These results imply that acrylamide which does not cause neurotoxicity in rats may alter blood viscosity if chronically taken.