In an article in the New England Journal of Medicine, two leading researchers warn that the entry of big companies like Microsoft and Google into the field of personal health records could drastically alter the practice of clinical research and raise new challenges to the privacy of patient records. The authors, Dr. Kenneth Mandl and Dr. Isaac Kohane, are long-time proponents of the benefits of electronic patient records to improve care and help individuals make smarter health decisions. But their concern, stated in the article published Wednesday and in an interview, is that the medical profession and policymakers have not begun to grapple with the implications of companies like Microsoft and Google becoming the hosts for vast stores of patient information in their data centers. The arrival of these new corporate entrants, the authors write, promises to bring "a seismic change" in the control and stewardship of patient information. Today, most patient records remain within the health system