In most cases, the viscosity of blood is measured after adulteration with heparin or EDTA. The aim of the present research was to derive an equation that can be used for determination of viscosity from biochemical data. Blood samples taken from seven healthy people were analyzed in biochemical laboratory and their viscosities were measured by adding EDTA as anticoagulant. Ten parameters of biochemical laboratory including blood cells (erythrocytes, leukocytes, thrombocytes) and their functional products that directly affect the blood viscosity were chosen. Several equations relating viscosity to those parameters were derived by using a computer program. According to the regression analysis of the functions derived, the viscosity equation was obtained. This equation can be used for determination of blood viscosity from classical laboratory analysis. The advantages of using the derived equation are elimination of anticoagulant addition and elimination of Fahraeus_Lindquist effect. After proving that the equation is acceptable for numerous people, apparent viscosity changes can be followed during any disease and successfulness of anticoagulant drugs can be investigated.