Arabinogalactan, or AG, is a fermentable fiber found in high concentrations in North American larch trees. It is also the active constituent of echinacea. AG has the potential to activate immune cells and to promote healthy microflora, including lactobacillus and bifidobacteria. Pure Encapsulations provides Arabinogalactan in 500 mg capsules. The recommended dose is 3 capsules per day.