Clinical pattern and dynamics of some biochemical indicators were observed in six four-year lambing ewes of the Improved Wallachian breed in the course of 32-day administration of magnesite fly ash. A daily dose of the tested fly ash with the content of 305,000 mg/kg magnesium amounted to 500 mg/kg live weight of sheep. The intake of concentrate mixture with magnesium content in the test sheep decreased by a third between the 12th and 20th day, by another half between the 20th and 26th day and the intake was minimum to nil during the last seven days of the trial. The decrease in the intake of concentrate mixture was accompanied by increased water consumption and by gradual inappetence for hay. Shaped droppings started to change their consistency to slurry consistency from the 12th day of observation. Thinner to watery consistency of excrements appeared in all sheep between the 15th and 20th day and diarrheas persisted in all animals until the end of the trial. The indicators of hematological profile did not show an undoubted relationship to the administration of tested magnesium, and the variations in the particular indicators observed during the trial were within the physiological range. Serum enzymes showed a significant increase against the starting values only in the concentration of alanine aminotransferase on day 20 and day 26 (p < 0.05 and/or p < 0.001). An increase in the proteosynthetic activity of hepatocytes signalled a statistically significant increase in total proteins (p < 0.05), total immunoglobulins (p < 0.05) and an insignificant increase in albumin content. Out of the analyzed mineral elements, magnesium content showed the most significant relationship to administration of industrial pollutants as its significant increase in blood serum, urine and droppings was observable since day 20 (p < 0.05, p < 0.01 and p < 0.001, respectively). The dynamics of calcium, phosphorus, potassium, sodium, iron, copper, zinc, molybdenum, arsenic and cadmium concentrations showed different patterns in the blood serum, droppings and urine of sheep in the course of magnesite fly ash feeding, and the evaluation of interactions with magnesium requires further studies.