What makes large corporations such aggressive purchasers of health care and what impact are they having on the health care market? Researchers at the JSI Research and Training Institute examined managed competition purchasing arrangements in large and multi-state corporations and identified what makes them such aggressive purchasers of health care. This study comprised seven case studies of diverse companies that have implemented managed competition in various ways, including Xerox, GTE, Digital, and General Electric. They also conducted case studies of three firms that have not adopted managed competition. The objective of this study was to document systematically how each firm implemented managed competition, including criteria used for choosing health care plans, whether financial incentives were applied, if there was participation with business coalitions, and whether there were procedures for monitoring the quality of, and patient satisfaction with, and health care delivered to employees.