Particle-fluid interactions in supersonic flows are relevant in many different applications e.g. the cold gas-dynamic spray process. The optimal application of the process is hindered by a lack of understanding of the particle-fluid interactions. To obtain detailed information on the particle-fluid interactions in these high-speed flows special high performance techniques are required. The present work is an investigation into the applicability of magnified digital in-line holography with ultra-high-speed recording for the study of three-dimensional supersonic particle-laden flows. An optical setup for magnified digital in-line holography is created, using an ultra-high-speed camera capable of frame rates of up to 1.0MHz. To test the new technique an axisymmetric supersonic underexpanded particle-laden jet is investigated. The results show that the new technique allows for the acquisition of time resolved qualitative and quantitative data on the fluid and particle dynamics. The potential for determining the three-dimensional particle positions using holographic reconstruction is also investigated. Five different focus functions used for depthwise location are tested using two different planar targets, a 10 × 10mm calibration grid and 120 μm particles on a glass plate. In the case with the calibration grid it is found that accurate determination of the depthwise position is possible. However, when applying the same technique to the particle target, significant problems are encountered. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.