Studied were both the acute and subchronic toxicity of technical tylosine phosphate (TP), produced at the Research Chemical and Pharmaceutical Institute, Sofia, used in combination with bentonite, known as Pharmasine TB. Pharmasine TB was practically untoxic for albino mice and birds at oral application. Neither toxic nor lethal effects were observed after giving it once, twice, and three times at a 2-hour interval at rates of 5 and 10 g per kg body mass. Calves and pigs also showed very good tolerance for the preparation at oral application. At prolonged application via the feed (30 days) in amounts of 0.5, 1.5, and 2.5 per cent (equal to 100, resp., 300 and 500 ppm with regard to tylosine in active matter) Pharmasine TB was shown to stimulate the weight gain on the basis of the better utilization of feed, having no unfavourable effect on the appetite, behaviour, clinical and biochemical composition of blood, and the morphologic structure of the viscera in pigs. Used in the same way with birds at the rates of 3, 5, and 10 per cent (equal to 450, resp., 750 and 1500 ppm with regard to tylosine in active matter) for a time period of 60 days the preparation did not lead to deviations in terms of the most clinical and morphological indices, however, it inhibited the weight gain by 3.2 to 8.1 per cent. According to the authors, this was due incomplete biologic value of the medicated feeds and their improper utilization because of the introduction of rather greater amounts of bentonite with Pharmasine TB.