Microcirculatory disturbances are observed frequently after restoration of the circulation in transplanted organ. The exact mechanisms responsible for impaired microcirculation during reperfusion are unknown. Erythrocyte deformability is an important factor maintaining the microcirculation. Red blood cells (RBC) (diameter 8 microm) passing through narrow capillaries (diameter 3-5 microm) undergo deformation due to shear stress present in the microcirculation. RBC with impaired deformability may even plug the capillaries. Immediately after completion a vascular anastomosis and restoration of blood circulation in the transplanted organ, RBC may be intimately exposed to the preservation solution. The aim of the present study was to investigate the effect of the preservation solution on deformability of RBC. Blood from five healthy volunteers was withdrawn by venipuncture from an antecubital vein. EDTA was used as an anticoagulant. RBC were isolated by 10-minute centrifugation (2500 rpm) to separate serum and buffy coat. RBC washed in normal saline were resuspended in autologous plasma, Bretschneider's histidine-tryptophan-ketoglutarate (HTK) or University of Wisconsin solution (UW) at an hematocrit of 20% for incubation at room temperature. After 30 minutes RBC deformability was measured using the shear stress diffractometer Rheodyn SSD to calculate the elongation indexes of RBC at various shear stresses. HTK caused a decrease in the deformability indices of erythrocytes at shear stresses from 0.3 to 1.2 Pa. Erythrocytes incubated with UW solution revealed a decrease in deformability index at all investigated shear stresses. HTK causes less deterioration of erythrocyte deformability compared to UW solution.