Studied were the acute, subchronic, and chronic toxicity of the Pharmachim tylosin tartrate as well as the tolerance of chicken broilers and turkeys. The mean lethal dose of the antibiotic at subcutaneous application to 28-32 day-old broilers was 620 mg/kg; the oral dose was 1500 mg/kg. In the case of 42-45-day-old broilers these values were 740 and 5400 mg/kg. The LD50 at i/v infusion for 75-77-day-old ones was 48 mg/kg. Beside the age and route of introduction toxicity was found to depend on the initial biologic activity of tylosin tartrate. The subcutaneous injection of tylosin tartrate at the rate of 30 mg/kg for 20 days did not lead to changes in the appetite, behaviour, growth, and structure of viscera. A 42-day treatment at the same rate, however, resulted in slightly manifested and fully reversible dystrophic changes in the liver and kidneys. Higher doses (90 and 150 mg/kg) led to transient depression, stunting of growth, and a rise of the urea level and the activity of blood transaminases as well as to moderate destructive changes in the liver and kidneys. The stimulation of growth and the improvement of feed conversion (without deviations in the clinical and biochemical indices of the blood and the structure and development of the viscera in broilers) were recorded after the application of a water-soluble formula of tylosin tartrate for a period of 98 days offered via the drinking water in amounts equal to or exceeding 2 to 4 times the ED50. Turkeys' tolerance for the preparation was evaluated as very good so far as single i/m injective applications were concerned in doses exceeding 3, 5, and 10 times the average effective rates, no differences in this respect being noted with the comparative use of tylosin tartrate produced by the Elanco firm.