Electron‐beam loading of a single‐cavity standing‐wave accelerator has been investigated experimentally and theoretically for the case of continuous injection over ten cycles. The particular cavity used was a 2.4‐m long right‐circular cylinder excited at 50 MHz in its TM010mode with an unloaded Q of 1.2×105. Beam currents were varied from 40 to 210 A, field strengths from 0.2 to 6 MV/m, and the energy of the ejected beam from 1 to 10 MeV. During beam injection the energy supplied per cycle to the accelerator by its power amplifiers was negligibly small compared to the energy absorbed per cycle by the injected electron beam. The energy extracted by the electrons was determined from cycle‐to‐cycle oscilloscopic observations of the decay of the accelerating field. Energy extraction per cycle was as great as 8% of that residing in the electromagnetic field at the time of beam injection. The results agree with predictions over most of the range of the experimental parameters when assuming paraxial trajectories. Disagreement with calculations, when using the same assumption, arose when there were serious departures from paraxial flow. The special case of injection of a sharply bunched relativistic electron beam is also reported. Here each 18‐MeV bunch contained about 1.7 &mgr;C and was about 6‐nsec long. When in an accelerative mode the electric field was degraded and energy flowed from the field into the beam bunches at a rate of about 0.6 BW. However, when the phase of the field was reversed to establish a decelerative configuration the electric field was enhanced, energy flowed coherently from the beam bunches into the field at a rate of about 0.6 BW. Within experimental uncertainties, these values agree with predictions.