Abstract: Haemodialysis (HD) is a procedure saving patient lives around the world, unfortunately it brings numerous complications. Oxidative stress is one of the major factors which lead to erythrocytes destruction during extracorporeal circulation. Repeated HD procedures destroy blood elements and the organism is not able to keep up with their production. 30 HD procedures on healthy sheep were performed to evaluate effects of such treatment. Oxidative stress study was performed together with an analysis of basic blood parameters and empirical assessment of dialyzer condition after the procedure. A reversible decline in absolute leukocyte count, during first 30 min of HD, was observed. Blood clots were formed in the area of the blood inlet and outlet of the dialyzer. Our results are consistent with outcomes presented throughout the literature specifically with respect to the effects observed in humans and will provide a basis to evaluate methods for blood protection during haemodialysis.