Erythrocyte microrheology changes were measured using cation-osmotic hemolysis (COH) in healthy rats and rats after 6 and 12 months of lead ingestion. Using COH, properties of two membrane constituents, spectrine membrane skeleton and membrane bilayer were studied. COH in rats after 12 months of lead ingestion was significantly lower only in the area with lower ionic strength (15.4-61.6 mmol x l(-1) of NaCl) (p < 0.01 resp. p < 0.05). No changes in COH were found after 6 months of continuous lead ingestion. The relation between cation-osmotic hemolysis and erythrocyte deformability is being discussed.