better yet, make your own kefir. Dom's kefir site is a good place for information on that. You can buy the starter cultures even on eBay, and there is someone who posts in the kefir grain forum who sells hers, she's MarilyntheKefirLady. It's got more healthy flora in it and more variety than yogurt. I personally feel fine on kefir, but don't digest yogurt very well.