Albino rats were used to study some remote side effects (total reproduction, embryotoxicity, and teratogenic action) of the Bulgaria Ronidazol-Pharmachim preparation, analogous to the one produced by the firm MS & D--USA (Ridzol 10 per cent water-soluble powder) used in veterinary practice as a prophylactic and therapeutic agent in the case of swine dysentery and turkey blackhead. It was found that at oral application of the amounts suggested as therapeutic means Ronidazol-Pharmachim did not show antifertility action. Orally (in the form of suspension), given over the entire period of pregnancy at rates of 20 mg per kg body mass (exceeding more than six times the recommended maximum of therapeutic doses) it did not produce embryotoxic and teratogenic effects. Certain hazards existed, however, of embryotoxicity (but not of teratogenic action) when used in doses that were twenty times higher.