Difficulties in the early stage detection of erythrocytes' microrheological abnormalities during the development of hypertension are connected with falling out of clinicians' opinion of persons with first signs of this pathology. It dictates the necessity of experimental investigations' fulfillment on laboratory animals with just developed hypertension in them. Eighty-seven of healthy male rats of Wistar line at the age of 2.5-3 months were taken into the investigation. Twenty-nine animals of them had experienced no impacts and composed the control group. Fifty-eight rats had hypertension developed by prescribing them cardio angionefo pathogenic semisynthetic diet. For the purpose of investigation biochemical, hematological, and statistical methods were used. As a result of hypertension, the rats turned out to have developed an increase of systolic and diastolic pressure. At regular exercise, on the treadmill, the rats were noted to have a gradual decrease of their values during 60 days of investigation to the normal level. During hypertension development lipids' peroxidation activated in rats' erythrocytes because the activity of their antioxidant protection weakened. When hypertension occurred in rats the erythrocytes-discocytes quantity in blood was found to have decreased. It was accompanied by an increase of reversibly and irreversibly changed erythrocytes quantity in the examined animals' blood. When hypertension occurred in rats a quick rise of erythrocytes' sum in aggregate was found and the rise in these aggregates' quantity was due to lowering of free erythrocytes' number. During experimental hypertension modeling, we noticed that there was a very early decrease in the quantity of erythrocytes-discocytes in the rat blood, and their level raised reversibly and irreversibly with the strengthening of their aggregative ability. It happened because of the weakening of erythrocytes' antioxidant protection, and activation of lipids' peroxidation in them.