The objective of the paper was to investigate clinical and laboratory findings in heifers subjected to magnesite flue dust stress. A 50-day experiment was conducted in clinical conditions on five two-year heifers of the Slovak and Red Pied breeds at the live weight of 331 to 420 kg. All animals received dietary Mg from the source of magnesite flue dust at a rate of 500 mg/kg live weight. The test flue dust came from dust separation from electrostatic filters and contained these main elements: Mg (88%), Ca (1.6%), K (0.36%), Na (0.26%), Fe (1.89%), Zn (0.0026%), Cu (0.000294%) and trace amount of P. The clinical health of the animals was evaluated daily. Samples of blood, urine and dung were taken before the first administration of flue dust, on days 12, 30 and 50 of the experiment. The counts of erythrocytes, leucocytes, hemoglobin concentration and hematocrit value were determined in blood. Enzyme activities (AST, ALT, GMT), concentrations of total bilirubin, albumin, total proteins and total immunoglobulins were determined in blood serum. Contents of Mg, Ca, P, K, Na, Fe, Cu and Zn in blood serum, urine, dung and of the test pollutant were determined by atomic absorption spectrophotometry on a Perkin Elmer apparatus (model 306, 1100). Profuse diarrhea was a dominant clinical symptom in the animals which appeared in individual animals between 24th and 48th hour from the first intake of magnesite flue dust. Diarrhea lasted alternately in all heifers until day 50 of the experiment. As for the analyzed parameters of hematological profile during administration of the pollutant (Figs. 1-4), Hb and Hk (P < 0.01) increased significantly in the investigated animals on day 12 in comparison with the initial values. Out of the enzymes, AST and ALT activities showed most readily the feeding of magnesite flue dust (r = 0.99 and r = 0.92, resp.), Figs. 5 and 6. Correlation relationships between magnesite pollutant administration and bilirubinemia dynamics during the experiment indicated the correlation r = 0.53 (Fig. 8), r = 0.36 (Fig. 9) for total proteins, r = 0.75 (Fig. 10) for albumin and r = 0.93 (Fig. 11) for total immunoglobulins. In comparison with the initial values, Mg concentrations in blood serum and dung significantly increased from day 12 of experiment (P < 0.01 - Fig. 13) and in urine from day 30 (P < 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)