A phase-conjugate holographic measurement system has been developed for the study of 3D fluid velocity fields. The recording system produces 3D particle images with resolution, signal-to-noise ratio, accuracy, and derived velocity fields that are comparable to high-quality 2D photographic PIV (particle image velocimetry). The high image resolution is accomplished by using low f-number optics, a fringe stabilized processing chemistry, and a phase conjugate play-back geometry that compensates for aberrations in the imaging system. In addition, the system employs a reference multiplexed, off-axis geometry for determining velocity directions using the cross-correlation technique, and a stereo camera geometry for determining the three velocity components. The combination of the imaging and reconstruction sub-systems make the analysis of volumetric PIV domains feasible. Recently, a new geometry for the HPIV system has been developed for imaging flows through thick-walled, curved windows. In the older geometry, there have been two sources inhibiting the use of windows: window scattering and window-induced aberrations. In the new system, these difficulties are avoided using side- scatter illumination of the particles and phase-conjugate reconstruction with a substitute window in place.