||A computer network was begun in June 1985 which extended the facilities of the Health Evaluation through Logic Processing (HELP) system from its base at the Latter-day Saint (LDS) Hospital, Salt Lake City, Utah, to offices of some members of the hospital's medical staff. Through the use of personal computers (PCs), data communication software and hardware, and the standard telephone network, the physicians and their staff were able to run HELP system laboratory, demographic, and other medical information programs directly from their offices or homes. A security system was installed a part of the network to prevent intrusion by unauthorized users and to monitor network usage by registered users. Analysis of network usage and security was performed during an initial 9-month study period, from June 1985 to February 1986, and during a 2-month follow up period in October and November 1986. Usage patterns of network participants corresponded to standard office hours. Peak usage occurred daily between 10:00 and 11:00 A.M., and weekly on Wednesdays. The number of network participants never exceeded 13; however, use of the network facilities by registered users during the follow up period was more than double that of the initial study period. Usage patterns varied greatly between individual uses (0 to 92.5 patient information reviews per month). There was no overt intrusion by outsiders. User restricted at least 81% of their reviews to patients for who they were attending, consulting, or affiliated physicians. More complete record of physicians probably would have revealed an even higher level of confidentiality. Users indicated that the network's major information review programs were useful to them, and that participation in the network increased their professional productivity. While over 100 physicians had network facilities available to them, the network was probably use only by a small subset of these physicians. This might have been due to three factors: (1) physicians' lack of knowledge of the network; (2) the usefulness of the HELP system features to only a subset of the hospital's medical staff; and (3) physicians' inexperience and reluctance in dealing with computers. By making its features better meet the need of the individual physician, participation in the physician information network may improve.