We studied the effect of active cytomegalovirus infection on histidine content in peripheral blood erythrocytes of pregnant women at gestation weeks 20-22 and its involvement into hemoglobin oxygenation. Using the histochemical technique developed by us, we studied the distribution of products of specific reaction for histidine in peripheral blood erythrocytes of pregnant women. The percentage of histidine-positive erythrocytes and their area were evaluated. The relationship between the distribution of the products of the reaction for histidine in peripheral blood erythrocytes of pregnant women and the titer of anti-cytomegalovirus IgG was revealed. The histidine content in peripheral blood erythrocytes of pregnant women with active cytomegalovirus infection was reduced, which impaired heme binding to globin and decreased the formation of oxyhemoglobin.