Ronidazol-Pharmachim (RPh) in the form of 10 per cent water-soluble powder was studied in terms of resistance to various values of pH of the surrounding medium, acute toxicity, the species-specific tolerance of various mammals of it, its subchronic toxicity and residual amounts with pigs. The preparation was found to be stable in water solutions (pH 5.0 to 9.0) in the course of at least 96 hours, and in n HCl--for more than a month. At oral administration LD50 of RPh was 34000 mg (2982 divided by 3876) per kg for albino rats weighing 150-200 g. At intraperitoneal injection in the form of pure substance LD50 was 1500 mg (1320 divided by 1690) per kg. With pigs at single oral application at the rates of 20, 60, and 180 mg/kg (= 20-30 times the ED50) RPh was tolerated with no changes in the behaviour and appetite. When used with the drinking water at rates of 60, 180, and 300 ppm in the course of 30 days there was no unfavourable effect on the gain and the blood picture and no injury of the structure of viscera of pigs. In concentrations of 180 ppm it was shown to stimulate the growth of pigs. The withdrawal time with pigs given RPh with the drinking water was at least 72 hours after the preparation was offered last.