This paper presents results from a quantitative characterization of the NO distribution in a SI engine fueled with a stoichiometric iso-octane/air mixture. Different engine operating conditions were investigated and accurate results on NO concentrations were obtained from essentially the whole cylinder for crank angle ranges from ignition to the mid expansion stroke. The technique used to measure the two-dimensional NO concentration distributions was laser induced fluorescence utilizing a KrF excimer laser to excite the NO A-X (0,2) bandhead. Results were achieved with high temporal and spatial resolution. The accuracy of the measurements was estimated to be 30% for absolute concentration values and 20% for relative values. Images of NO distributions could also be used to evaluate the flame development. Both the mean and the variance of a combustion progress variable could be deduced. The engine used in the investigation was a one cylinder version of a Volvo N1P engine equipped with good optical access. Using the same engine and the same operating conditions, data on the in-cylinder flow field was also obtained using particle imaging velocimetry.The comprehensive and detailed data base generated in the present work is currently being used for detailed validation and improvements of models for numerical simulation of engine combustion and emission formation.