The effect was studied of sodium monensinate dosed 125 mg pro die and given to feeder cattle on the health condition and some clinico-biochemical parameters in view of the energy metabolism. The experiment was performed under current farming conditions in a pavilion fattening house. The experiment, which lasted 367 days, was conducted with 985 bulls of the Bohemian Spotted breed. Ten animals from the experimental and ten animals from the control pavilion were subjected to detailed clinical and clinico-biochemical examination. The feed ration was based on corn silage with an additive of dried poultry litter and concentrates. The additive was administered in the concentrate mixture, 125 mg per head/day. The health condition of the bulls was good during the whole period of study, and except several cases where neck chain wounds were observed, or small traumatic alterations on the extremities, no health disorders occurred. Some clinico-biochemical parameters of the blood were followed to study the metabolic processes and health condition. pH, pCO2, BE, SB were studied to find out the acid-base relations of the blood. As to the energy metabolism, the levels of glucose, total protein, urea, nonesterified fatty acids, triglycerides, cholesterol and total lipids were followed. Among other hematologic parameters studied there were hemoglobin, hematocrit, beta-carotene and the levels of glutamate-oxalacetate transaminase and glutamyl-transpeptidase in relation to liver metabolism. During the period of study, increased urea levels were found in the experimental animals, and on the other hand lower levels of free fatty acids and triglycerides in the blood serum. No significant changes in the other studied parameters were observed in the course of the experiment. It can be stated according to the obtained results that sodium monensinate did not influence negatively the studied clinico-biochemical parameters nor the health condition.