Studied were ampicillin-Na and ampicillin-trihydrate of an 800 IU/mg activity. The first was applied in the form of aqueous solution, and the second--in the form of an aqueous suspension. It was found that i/m injection of ampicillin-trihydrate to sheep (10 and 25 mg/kg) and lambs (10 and 20 mg/kg) led to the elimination of the antibiotic via the urine in bacteriostatic concentrations for 48 hours, while the application of ampicillin-Na under the same conditions led to its elimination in the course of 24 hours. In lactating ewes ampicillin was eliminated through the milk secretion. At a single muscular injection to ewes at the rate of 25 mg/kg ampicillin-Na was eliminated via the milk in higher concentrations, reaching a peak volume at the fourth hour--0.75 mg/cm3, for a shorter period of time (up to the 14th hour) as compared to ampicillin-trihydrate (up to 24th hour) when used in the same dose. When applied to laying hens directly through the crop at 60 mg/kg in the course of six days it was excreted during treatment and two days later via the eggs in therapeutic concentrations.