The change in human red blood cell microrheology in different glutaraldehyde concentrations (1.5, 3.0 and
$5.0 \times 10^{-6}$
mol
$\,$
l
$^{-1}$
) was studied. The method of millipore filtration was compared with the method of cation‐osmotic hemolysis. The obtained results revealed that the prolongation of the erythrocyte filtration time correlated with the curve shifts found in cation‐osmotic hemolysis. Contrary to the filtration method, significant differences between two lower concentrations of glutaraldehyde (1.5 and
$3.0 \times 10^{-6}$
mol
$\,$
l
$^{-1}$
) were found. Therefore, we conclude that the cation‐osmotic hemolysis is more sensitive than the filtration method in determining the red blood cell deformability.
