This paper presents preliminary results of studies of the feasibility of applying electro-optical diagnostic techniques to diesel engine research. A 2-cycle, 3-cyl, diesel engine was modified by installing quartz windows in the combustion chamber to provide optical access. Techniques investigated include photography, holography, laser resonance absorption spectroscopy, and laser velocimetry. Droplet formation, breakup, and combustion can be observed in the combustion chamber in three dimensions using holography. The same hologram can be used for particle sizing and flow visualization studies. Formation of certain hydrocarbons can be observed in real time with resonance absorption, using a tunable He-Ne laser. It has been established that laser velocimetry can give components of air velocity in the combustion chamber of a motored diesel engine. The techniques described are currently being developed for application to diesel engine research and to evaluation of a stratified charge spark ignition engine.