The search for protective substances that can be used during red blood cell thawing and the study of their effects on red blood cells contribute to increasing the number and quality of viable cells after the cryopreservation cycle. We studied the effect of posthypertonic shock and amphiphilic compounds on the shape and eryptosis of human erythrocytes. The method of flow cytometry was used, this allows analyzing two parameters simultaneously, which increases the efficiency of research. The shape was assessed by the sphericity index (SphI), and eryptosis by the redistribution of phosphatidylserine to the membrane outer surface. It has been shown that sodium decylsulfate and chlorpromazine reduce erythrocyte damage in posthypertonic shock by 3.6 and 4.2 times, respectively. Sodium decylsulfate helps to preserve the shape of cells (SphI coefficient remains the same), while when chlorpromazine is used, the shape changes towards spherical (SphI coefficient changes 2 times). The study of the level of Annexin V FITC binding to phosphatidylserine in outer layer of membrane revealed a concentration-dependent increase in fluorescence when sodium decylsulfate was used, indicating a disorder of the bilayer asymmetry. In contrast, chlorpromazine did not change the distribution of phosphatidylserine. Comparison of two parameters of cell viability - the sphericity coefficient and anexin binding - allowed us to choose the conditions that are optimal for the use of the studied protective substances. Namely, it is advisable to use the lowest effective concentration of sodium decylsulfate (200 mcmol/l) for protective purposes. This ensures the preservation of the cell shape and minimal impact on the membrane asymmetry.