Measurements of temperature and nitrogen density and the fluctuations of these quantities have been made in a combusting engine. The measurements were made by applying pulsed, spontaneous laser Raman spectroscopy. This nonintrusive technique demonstrates one cubic millimeter spatial resolution and essentially instantaneous temporal resolution (10−8 second). Densities were determined by measuring the Stokes vibrational scattering of nitrogen, and the temperatures were determined by measuring the ratio of anti-Stokes to Stokes scattering. The diagnostic technique is described and its accuracy analyzed.Temperatures and densities at two locations, over crank angles covering the compression and expansion strokes, for four equivalence ratios are presented. Typical temperature probability distributions are also presented.