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This research demonstrates the capability of the Laser Doppler Anemometer (LDA) for making measurements inside a piston-engine cylinder. The backscatter mode of LDA operation, requiring only a single window in the cylinder, was used. An ensemble-average data-processing technique has been developed to analyze the raw velocity-crankangle data. Single-component measurements of mean velocity and rms velocity fluctuation at a single point are presented as functions of crankangle for three engine speeds. A comparison of motored and fired results is shown for one engine speed. Measurements of two components of velocity at several locations show the basic vortical nature of the flow field in this particular engine.