The increasing availability of intermediate and high voltage transmission electron microscopes, together with recent improvements in video recording equipment, have led to renewed interest in in situ dynamic experiments. To alleviate the problems encountered in preparing TEM specimens with the awkward geometries required for straining stages, a jet polishing technique has been developed which allows the use of a conventional twin-jet electropolishing unit, with all its attendant advantages. A pair of Teflon sheet inserts, with rectangular openings cut to a specific shape and size, are used in the conventional specimen holder. Specimens with elliptical holes close to the center of the gauge section, and with large electron transparent areas at both ends of the long axis, are produced routinely and rapidly. Samples of many annealed metals, such as brass, molybdenum, and aluminum, prepared by this method are stronger, and can be handled more easily, than those prepared by conventional methods.