Blood cells quickly react to different physiological and pathological processes in the organisms of pigs. Functional condition of erythrocytes is the most successful biological model for studying the dynamics of changes happening in the organisms of pigs. There has been carried out the analysis of hematological condition which showed that during the experiment in the animals under the condition of diinvasion Balantidium coli-Candida spp. there was a cyclic change of morphometric indexes of erythrocytes of peripheral blood. In the first 20 days there was marked an increase in the number, size, volume of the erythrocytes and the hematoglobulin inside of them, which is obviously connected with the compensatory reactions resulting in the intensification of hematopoiesis. On the 30th day and up to the end of the experiment there was marked a reduction of these parameters connected with the change of biochemical processes in the membranes of the erythrocytes and with the reduction of their resistance.