Two feed mixtures were produced, each containing the antimicrobial preparation Carbadox and different amounts of furazolidone. Their fortnightly administration in starters to piglets weaned at the age of 25--31 days prevented mortality and stimulated somatic growth and feed utilization. Premix with a higher content of furazolidone markedly depressed the clinical symptoms of gastro-enteritis and reduced the number of the haemolytic germs of E. coli in the contents of the duodenum and jejunum. The presence of furazolidone in the feed completely eliminated enteral disorders and delayed the onset of the disease, or alleviated its course, in cases of severe diarrhoea, which killed, in the control group, the piglets of the same litter. Weight gains were significantly increased, particularly in the first post-weaning week, the difference from the control being up to 520%. Almost 0.5 kg of the COS 2 starter was saved per 1 kg of piglet live weight gain. Under the current farming conditions of five agricultural enterprises the weight gains during the ten days of the administration of the medicated feed were increased, on an average by 0.84-1.32 kg. In herds where the untreated piglets put on less than 1 kg the gains were increased by 96--124%. It is recommended to administer the new-developed medicated premix to prevent losses due to alteration of the intestinal microflora in early-weaned piglets.