Field instrumentation represents a class of distributed interactive simulation (DIS) participants which consists of real people operating real equipment, an application domain known as live simulations. These simulation have been conducted for many years at the nation's military training centers and test and evaluation ranges. Though in the past these activities have been carried out with great success, recent initiatives have lead to the desire to perform exercises where these live participants interact with simulated participants. This represents a formidable challenge and will be successfully addressed only if the major problems are clearly understood. This paper lists and describes the most significant issues that have been identified by the DIS Field Instrumentation working group.