Highly efficient Volume phase holographic (VPH) gratings do not lend themselves to use in existing spectrographs except for grism spectrographs where VPH grisms can be designed that disperse but do not deviate the light. We discuss our program to outfit existing spectrographs [the Imaging grism instrument (IGI) on the McDonald Observatory Smith Reflector, and the Hobby-Eberly Telescope Marcario Low Resolution Spectrograph (LRS)] with efficient VPH grisms. We present test data on sample gratings from Ralcon Development Lab, and compare them to theoretical predictions. We have created a simple test bench for efficiency measurements of VPH gratings, which we describe. Finally we present first results from the use of VPH grisms in IGI and the LRS, the latter being the largest grism ever deployed in an astronomical spectrograph. We also look forward to using VPH grisms in the LRS infrared extension, which covers the wavelength range from 0.9 to 1.3 microns.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.