As we enter the 21^st century, military medicine struggles with critical issues. One of the most important issues is how we train medical personnel in peace for the realities of war. In April 1998, the General Accounting Office (GAO) reported, "military medical personnel have almost no chance during peacetime to practice battlefield trauma care skills. As a result, physicians both within and outside the Department of Defense (DOD) believe that military medical personnel are not prepared to provide trauma care to the severely injured soldiers in wartime…." With some of today's training methods disappearing, the challenge of providing both initial and sustainment training for almost 100,000 military medical personnel is becoming insurmountable. The "training gap" is huge, and impediments to training are mounting. For example, restrictions on animal use are increasing, and the cost of conducting live mass casualty exercises is prohibitive. Many medical simulation visionaries believe that four categories of medical simulation are emerging to address these challenges: PC-based multimedia, digital mannequins, virtual workbenches, and Total Immersion Virtual Reality (TIVR). TIVR is the most effective solution, although it is the most expensive and will take the longest time to develop. To address the TIVR challenge, the Medical Simulation Training Initiative (MSTI) is a visionary military program that seeks to develop a multi-functional simulation platform based on a Personal Computer, with 3-D holographic imaging of anatomic compartments and/or body structures. We envision the interface to be an exoskeletal robotic device, haptic gloves and other interactive surgical devices. Success requires several key components. First, a strategic plan. Second, single-agency integration of research efforts. Third, research in "enabling technologies", e.g., tissue modeling, haptics integration, physiological representations and overall systems architecture. This is necessary to develop realistic representations of medical procedures as a basis for simulation. Fourth, careful efforts among domain experts in their own fields, e.g., physicians, nurses and "combat medics", working side by side with engineers, computer scientists, designers, experts in education and training, human factors engineers, and managers, to ensure useful products for end users. MSTI will provide a risk-free, realistic learning environment for the spectrum of medical skills training, from buddy aid to trauma surgery procedures. This will, in turn, enhance limited hands-on training opportunities and revolutionize the way we train in peace…to deliver medicine in war. High fidelity modeling will permit manufacturers to prototype new devices before manufacture. Also, engineers will be able to test a device for themselves in a variety of simulated anatomical representations, permitting them to "practice medicine."