The membranes of the erythrocytes are covered with different kinds of proteins determining decisively the aggregation and disaggregation properties of erythrocytes. Morbid changes in the human body are reflected by changes in the kind and concentration of these proteins and this way by the aggregation and disaggregation behavior of erythrocytes. Light scattering measurements were used for the investigation of these changes comparing healthy volunteers and patients with different diseases. The whole blood samples were analyzed using a rotating coaxial cylinder system in combination with a special method for data processing. The erythrocyte aggregates were destroyed completely without injuring the cell membranes by shear forces arising during the cylinder rotation. In this paper the results of aggregation and disaggregation analysis of erythrocytes in whole blood samples of healthy volunteers and patients suffering different diseases are presented. The method of erythrocyte aggregation and disaggregation measurements is compared with blood sedimentation measurements.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.