Studied was the preparation thiabendazole-Pharmachim (TBZ-Ph), produced by the Economic Corporation "Pharmachim". In some of the experiments TBZ-Ph was comparatively studied with the Merck & Sharp and Dom preparation (TBZ-MShD), Switzerland. It was found that the light absorption maximum of TBZ-Ph was at 302 nm. Thermostability studies revealed that the preparation was comparatively stable in the course of 6 months at room temperature and at 4 degrees and 40 degrees C. When stored in the form of 1 per cent medicated feed at room t degrees, 4 degrees, and 40 degrees C it showed no deviations as against the check samples over a period of 70 days. TBZ-Ph was shown to possess slight photosensitivity; it was not hygroscopic. In oral administration to sheep and pigs at the rate of 100 mg per kg body mass, in the form of a 10 per cent water suspension TBZ-Ph was absorbed through the gastro-intestinal membrane. It was retained in the blood serum of sheep up to the 24th hour. The preparation was shown to gain access to almost all viscera and striated muscles, persisting in them for some twenty days. Following the oral application in a dose of 100 mg/kg it reached the mammary gland of lactating ewes and was detected in the milk in maximum concentrations as early as the 3rd hour (5.8 to 12.3 ppm); in the course of the following hours concentrations dropped, and in individual animals the preparation was traced up to the 96th hour.