Relativistic electron beams were generated in a gas-loaded foil-less magnetized diode. The helium gas was employed to fill the diode, and the experimental results have shown that the diode operated normally without the closure problem when the gas pressure was below a certain value (typically, 100 mTorr in the presence of an externally applied guide magnetic field). It has been observed that the current of the electron beam could increase with increasing the gas pressure, and that the presence of helium gas could reduce the operating voltage of the diode producing an electron beam with lower kinetic energy, which implies a decrease in the diode impedance. The externally applied magnetic field along the axial direction also exerted an influence on the electron-beam generation in the gas-loaded diode. © 1998 American Institute of Physics.