A factor, designated the, "T" factor, was found to be an accessory growth substance for Lactobacillus fermen-turn (L36). Among known vitamins, growth factors and miscellaneous materials, only thiamine partially substituted for the "T" factor but is thought not to be identical with it. The "T" factor is found in tomato juice (hence "T"), liver, string beans, carrots, beets, onions, cabbage, peppers, spinach and orange juice.