Several next-generation air defense missiles will use dual- mode guidance systems that simultaneously employ RF and IR sensors to obtain significant improvements in guidance performance. These missiles will require sophisticated hardware-in-the-loop test facilities to provide controlled signal environments to each sensor. Such test facilities allow accurate characterization of RF and IR sensors as well as the development and validation of guidance algorithms. Two approaches for dual-mode hardware-in-the-loop testing used at The Johns Hopkins University Applied Physics Laboratory (APL) are `electrically connected' and `collocated.' Each uses a common central computer to precisely coordinate RF and IR environment generators. The electrically connected approach requires disassembly of the guidance section and locating RF and IR seekers in different rooms. Extended electrical interfaces couple the seekers to the missile's guidance computer. This arrangement is well suited for development testing where flexibility is the primary concern. In the collocated configuration, disassembly of the guidance system is not needed since the RF and IR test environment generators are built into a common facility. This noninvasive configuration is useful in identifying and resolving performance issues associated with an integrated guidance system. This paper describes the capabilities and status of the collocated dual-mode Guidance System Evaluation Laboratory developed at APL.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.