Source Naturals Acidophilus is a specially cultured strain of viable, freeze-dried Lactobacillus acidophilus. The body relies on Òfriendly floraÓ residing in the intestines for internal protection against putrefactive yeasts and bacteria, which can secrete toxins and hoard vital nutrients. Acidophilus supports colon health by altering the microflora ecology and favoring ÒfriendlyÓ flora. It also manufactures some B-vitamins, especially folic acid.