Introduction: Due to the absence of internal structure, the shape of erythrocytes is determined by erythrocyte membrane properties, therefore, the observation of the erythrocyte form is often used to investigate the effect of chemicals on cell membranes. The most common erythrocyte membrane responses to external factors are echinocytosis and stomatocytosis. Purpose: We wanted to create a method by which, on the basis of a change in the shape and number of erythrocytes, the effect of the substances on the cell membranes would be compared. As an example, three substances derived from the blood of the patient with Alzheimer's disease (labeled by number 1) and two healthy donors (34 and 39) were used. Methods: The substances were added to the erythrocyte suspension and the samples were observed under the optical microscope immediately after the addition of the substance, after one hour and 24 hours. During the observation we made a series of images of each sample that was used to analyze the shape and number of cells. We separated the stomatocytic, discocytic, echinocytic and spherical form of erythrocytes. Samples were compared with descriptive statistics. The results: In the fresh blood of control samples, they are mostly discocytes, later it comes to spontaneous echinocytosis and after one day, even hemolysis. In the samples with added substances 34 and 39, this process was faster than in control samples, and spherocytes were also formed. The process was the fastest in the sample with the added substance 39. In samples with substance 1, the discocytes were longest preserved. According to the number of cells per picture, the sample 34 did not differ from the control, the sample 39 contained fewer cells than it, and the sample 1 more. In the samples with substance 1, the cells were joining in aggregates. Discussion and conclusion: The analysis of the forms has shown that the effects of various substances on erythrocytes can be distinguished from the control samples as well as among themselves. The substance obtained from the blood of a patient with Alzheimer's disease in the remission phase had the greatest effect on the spontaneous course of echinocytosis in the samples. We also found some weaknesses in the method, especially in the preparation of observation chambers.