The enhancement of energy loss of short pulses of electrons in plasma has been experimentally observed. An enhancement of up to3.5×104over single-particle losses was observed when a 15 ps electron bunch was injected into a preformed target plasma with an electron density of approximately1013 cm−3.This matches the theoretical prediction that the energy loss should be enhanced when the temporal duration of the electron bunch is approximately equal to&pgr;/&ohgr;pe,where&ohgr;peis the plasma frequency of the target plasma. 2D numerical simulations are in good agreement with the observations. ©1997 American Institute of Physics.