We examine the production of counterstreaming electrons associated with parallel fields along auroral field lines through the use of computer simulation. We use a 2 1/2 -dimensional (two spatial and three velocity dimensions) electrostatic particle algorithm and auroral boundary conditions to set up a self-consistent V potential structure. The simulation produces signatures of counterstreaming electrons resembling those observed by the Dynamics Explorer 1 (DE 1) satellite. The main signatures are as follows: (1) the phase space contours of the electron distribution function are elongated along the V∥ axis, and (2) the energy of electrons streaming in the upward direction is comparable to the energy of the accelerated electron beam. The simulation indicates that a portion of the accelerated electron beam is trapped by large amplitude electrostatic waves produced through the two-stream instability. Strong wave-particle interactions then thermalize the trapped electrons to produce suprathermal electrons streaming in the direction opposite to that of the accelerated electron beam. These results suggest a possible mechanism of producing a counterstreaming electron fluxes through nonlinear processes of the two-stream instability.