How does increasing HMO market share in a geographic area affect the acquisition and use of MRI technology? This project examined the ways in which HMO market penetration influences the adoption and use of MRI technologies. In particular, the researchers examined: 1) the extent to which variation in market-level HMO activity is associated with market-level MRI availability; 2) the extent to which variation in the influence of HMOs on hospitals is associated with variation in hospital MRI adoption decisions; 3) the extent to which variation in market-level procedure volume is associated with variation in market-level HMO activity and MRI availability; and 4) the extent to which variation in the number and combination of diagnostic imaging procedures used for patients in different markets is associated with market-level HMO activity and MRI availability. The objective of this study was to shed light on the ways in which HMO market share interacts with other parts of the health care delivery system. In addition, since the adoption and use of technology are likely to contribute significantly to health care spending, understanding the effects of managed care on technology may also clarify the effects that the continuing shift towards managed care will have on health care costs.