Sometimes a bit of bacteria can be just what the doctor ordered. If you prize yogurt for its "active cultures," you know what I'm talking about. Now a new study, published in the September 21 st online issue of Nature, suggests that good bugs might even hold diabetes at bay. Type I diabetes is caused by an immune system malfunction. Basically, the immune cells that usually chase after bacteria instead attack the pancreas, wiping out the cells that produce insulin. So researchers decided to see what would happen if they reigned in the immune response in mice that are prone to diabetes. As expected, they found that the animals were less likely to develop the disease. But the effect depended entirely on the critters having a normal complement of friendly bacteria in their intestine. Mice that were raised in a totally sterile, germ-free environment were rampant diabetics. But simply treating those mice with a cocktail of bugs found in most mammals' bellies cured the disease. How bacteria in the intestine can stave off diabetes is not yet clear. But the finding could lead to some interesting new treatments. In the meantime, remember that we can't live without the stuff that lives in us.