Blood transfusions can go terribly awry if our immune systems detect red blood cells that possess foreign surface sugars: type A's α-1,3-linked N-acetylgalactosamine or type B's α-1,3-linked galactose. Now, clipping off a red blood cell's type A and type B sugars to make the more universally accepted O-type blood cell has been achieved with two newly discovered bacterial glycosidases (Nat. Biotechnol., DOI: 10.1038/nbt1298). Previous strategies to trim these potentially immunogenic sugars from A-, B-, and AB-type blood have not found clinical use because of enzymatic inefficiency. The glycosidases identified by a team led by Henrik B. Clausen at the University of Copenhagen do the conversion with excellent yield at neutral pH. The authors point out that "the availability of these bacterial enzymes should allow efficient and cost-effective enzymatic conversion of blood group A, B, and AB red blood cells to universal red blood cells." Furthermore, one such enzyme, α-N-acetylgalactosaminidase, has both an unusual catalytic mechanism and a novel glycosidase structure.