The McKesson Corporation is America’s largest health-care provider.  It encountered even more growth on its purchase of U.S. Oncology at the end of 2011. Its primary activity remains in distribution though with a staggering third of all medicines used in the country being processed through it. It also boasts a major role in health care information systems with over 70 percent of America’s big market hospitals digitizing prescriptions and medical records through its technology.