AbstractDistributed simulation applications often rely on middleware to provide services to support their execution over distributed computing environments. Such middleware spans many levels, ranging from low‐level support for data transmission through object request brokers to higher level, simulation specific functionality such as time management. We discuss design alternatives for realizing such middleware for hard real‐time distributed simulations such as hardware‐in‐the‐loop applications. We present the results from tests of a prototype implementation of real‐time Run‐Time Infrastructure middleware. Its performance is compared with a non‐real‐time implementation. The context for this work is the High Level Architecture standard that has been defined by the U.S. Department of Defense. Copyright © 2004 John Wiley & Sons, Ltd.