Active components responsible for increased synthesis levels of levorin, a polyenic antibiotic in mixed cultures of an actinomycete and a yeast-like fungus C. tropicalis were isolated from the fermentation broth. Component I identified as succinic acid increased the levels of the antibiotic production by 40-50 per cent. Component II found to be lactic acid increased the antibiotic production levels by 20 per cent. Component III, a mixture of nonidentified substances of the amine nature stimulated biosynthesis of levorin by 20-25 per cent. Addition of a mixture of succinic acid and N-methyl glucosamine to the nutrient medium provided increase of the antibiotic activity of the fermentation broth up to 175-185 per cent as compared to the control.