The influence of feedstuffs treated with ionizing radiation on the nutrition of dogs was tested in four groups of animals. Two groups were administered for 90 days a ration, the main part of which (VETACAN meat feed mixture and VETAVIT loose feed mixture) was irradiated with radioisotope Co 60 of the intensity of 25 kGy/kg, in other two groups of dogs the nonirradiated ration was used for the same time period. The control groups of dogs were put together for these two diets. The laboratory examination of irradiated feedstuffs confirmed their complete microbiological and mycological intactness. However, the irradiation brought about a significant 35% degradation of essential amino acids with an increase of ammonia nitrogen, destructive changes in the lipid component of feedstuffs and a partial decomposition of the saccharide part of the VETAVIT feed mixture, expressed by the acidity of water extract. The sensory evaluation of irradiated feedstuffs did not show any perceptible alterations. The haematological examination of the blood of animals, which had been administered irradiated feed rations, demonstrated a significant negative influence on the blood picture. The biochemical examination of the blood serum and plasma revealed that total proteins of experimental dogs dropped and the creatinine level was also significantly decreased. Neither was the level of carbohydrate nutrition nor the energy saturation affected by irradiation. The glucose levels in the blood serum of dogs fluctuated within the range of physiological reference values. The growth of free ammoniacal bases of feedstuffs, evoked by ionizing radiation, conditioned obviously the level of actual pH of blood in dogs as determined in this study. The destruction of lipoid fraction in the feedstuffs induced a decrease in the activity of lipophile retinol and thus the biological value of feeds was impaired. The biochemical examination of ALT, AST and ALP enzyme activity did not show any increased activity of parenchyma, in particular of liver cell. A decisive role of the biological quality of feed ration for utilization of some minerals was demonstrated by a significant decrease of the magnesium level in animals administered irradiated feed rations without any biological supplementation. On the contrary, the potassium, calcium and phosphorus levels did not reflect this dietary difference between the groups.