  An electron distribution with a temperature anisotropy T_par/T_perp > 1 can
lead to the Electron Firehose instability (Here par and perp denote directions
relative to the background magnetic field B_0). Since possible particle
acceleration mechanisms in solar flares exhibit a preference of energizing
particles in parallel direction, such an anisotropy is expected during the
impulsive phase of a flare. The properties of the excited waves and the
thresholds for instability are investigated by using linearized kinetic theory.
These thresholds were connected to the pre-flare plasma parameters by assuming
an acceleration model acting exclusively in parallel direction. For usually
assumed pre-flare plasma conditions the electrons become unstable during the
acceleration process and lefthand circularly polarized waves with frequencies
of about the proton gyrofrequency are excited at parallel propagation.
Indications have been found, that the largest growth rates occur at oblique
propagation and the according frequencies lie well above the proton
gyrofrequency.
