Abstract : The influence of longitudinal combustion instability on the gross behavior of solid-propellant rocket motors has been studied in some detail at the Canadian Armament Research and Development Establishment. From pressure recordings, it was inferred that traveling gaseous compression waves, ranging in strength from weak-but-finite to shock discontinuities, were associated with the instability. In the present investigation, optical techniques are being applied to studies of the unsteady flow field, the combustion processes, and the regions of interaction. The initial phase is concerned with acquiring a time-resolved description of the flow processes occurring in a small windowed rocket motor during high-amplitude combustion instability. This note describes preliminary results that provide a semiquantitative description of the gross aspects of the internal flowfield and that clearly show the existence of a propagating shock front. (Author)