The objective of the study was to determine selected indicators of the internal environment in individual cattle categories during the period of fattening to evaluate the relation of the individual blood components to the growth intensity and qualitative indicators of the meat. The trial involved half-siblings -bulls, heifers and steers housed in one stable. The threesome always had a common father. During the trials the live weight was monitored and blood samples were taken on days 310, 403, 448, 479, 512, 554 and 618 of age. The concentrations of total proteins, glucose, total cholesterol, urea and catalytic concentrations of ALP, ALT, AST, calcium, inorganic phosphorus, magnesium and copper in the blood plasma were assessed. In all cases the levels of indicators of the internal environment were within the range of the physiological values for the respective age category. Compared to bulls and steers, the concentration of total plasma cholesterol of the heifers was significantly higher (p < 0.05 and p < 0.01, respectively). The last samples were taken prior to slaughter of the animals and the individual components were correlated with the nutritional values and meat indicators; the correlation between the amount of glucose and urea in the blood serum and the tenderness of the meat was significant (p < 0.05 and p < 0.01). The correlation between the concentration of proteins in the blood plasma, the level of nitrogen or total protein in the muscles, the water-holding capacity and meat tenderness was positive. The study provides a basis for implementing helpful adjustments in current cattle management practises. Blood indicators presented in this paper can be added to existing knowledge to benefit veterinary research and clinical evaluations. , cattle, blood, enzymes, total proteins, glucose, phosphorus, magnesium, copper, cholesterol, water-binding capacity, shearing tests The gradually increasing milk efficiency of dairy cows in the Czech Republic and the quota limitations in milk production resulted in reductions in the numbers of dairy cows and in the total number of reared cattle. One of the options of how to maintain the numbers of cattle in the country is to rear cows that do not produce market milk. Therefore beef cattle breeds are increasingly reared. An important aspect when extending this type of rearing is to be aware of the effect of the breeding conditions on the animals and to ensure their good health, optimal efficiency expressed by their growth capacity with regard to the production of the required amount and quality of animal products. If we are to create optimal conditions that would correspond to the current requirements of individual animals, we must draw as much information as possible about the internal environment, which reflects these effects and, above all, indicates the level of nutrient, mineral and vitamin supply required, which at the same time shows the functional condition of the animal. Changes in haematological and biochemical blood indicators of various cattle categories ar...