The secondary emission of electrons from tungsten, steel, aluminum, and graphite was studied as a function of the energy of the bombarding primary electrons in the range from 30 kilovolts to 340 kilovolts. The ratio of secondary to primary electrons was found to diminish with increasing primary energy and to increase with the atomic number of the target material. Thus, with aluminum the ratio diminished from 0.25 at 50 kilovolts to 0.17 at 200 kilovolts, while with tungsten it diminished from 0.73 to 0.62 in the same voltage range. Study of the energy distribution of the secondary electrons showed a percentage with energies less than 20 volts. Most of the remainder had energies greater than the available 800-volt repressor potential and resulted mainly from elastic nuclear scattering, particularly in the case of targets of high atomic number.