The ability of canine strain Enterococcus faecium EE3 to survive in healthy dogs and its effect on microbiological and biochemical parameters was determined. The strain was individually applied to 11 dogs per os at a dose of 10(9) CFU/mL (differed from 2 to 3 mL) for 1 week and persisted in feces for 3 months after cessation of its administration (reaching average concentration of 6.83 +/- 0.95 log CFU/g). Seven d after administration, a decrease in staphylococci and a significant decrease in Pseudomonas-like bacteria was observed. On the other hand, concentration of lactic acid bacteria increased but the growth of E. coli was not influenced. In the blood samples of dogs after 0-1 d (before application) and the blood samples 1 week after application, total lipids decreased in 8 dogs; the total protein also decreased. The levels of cholesterol were brought to the physiological level, i.e. in blood samples with low cholesterol values it increased to the physiological level and in those with high levels it decreased; cholesterol was not influenced in 3 dogs.