Practical details of a scanning low energy electron probe (SLEEP) are described. The SLEEP incorporates a demountable electron optical system (EOS) with a triode type gun, an electrostatic and a magnetic lens, and a magnetic scanning system. The cathode is at approximately ground potential. The EOS can be operated satisfactorily at anode voltages between 500 V and at least 10 kV and produces an electron beam of between 5 and 25 &mgr; in diameter which can be scanned over a mesh electrode of 5 cm in diameter. The specimen is placed beyond the mesh electrode but close to it and the electron beam decelerates in the region between mesh and specimen and is partially reflected from the specimen. Electronic circuits for measurements and the control of the EOS are described, and the practical limitations to be expected are discussed briefly. Instruments of this type can be used to make quantitative measurements of electrical parameters. Applications of the SLEEP are discussed briefly.