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A photoelectron gun as a source of a photoinduced, monoenergetic (energy spread <0.5 eV), well-collimated (divergence <0.5 deg), sharp (diameter <0.7 mmat the 1/elevel), and ultrashort (500 fs)bunch of electrons to be used for time-resolved electron diffraction (TRED) experiments is computer designed, assembled, and tested. In single-shot mode, it generates up to 103of 30 keV electrons, and the electron pulse can be either measured in streak mode or focused onto a solid state target chosen from a set of interchangeable targets. High temporal resolution enables measurement with femtosecond precision of the diffraction pattern perturbation after the exiting laser radiation drops onto a target. Demonstration experiments with a 300-Å A1 target in transmission-type mode result in diffraction images of reasonable quality under accumulation of up to 4×104500-fs photoelectron pulses. © 1998 Society of Photo-Optical Instrumentation Engineers.