  We formulate a general approach which describes statistics of current
fluctuations in mesoscopic coherent conductors at arbitrary frequencies and in
the presence of interactions. Applying this approach to the non-interacting
case, we analyze frequency dispersion of the third cumulant of the current
operator ${\cal S}_3$ at frequencies well below both the inverse charge
relaxation time and the inverse electron dwell time. This dispersion turns out
to be important in the frequency range comparable to applied voltages. For
comparatively transparent conductors it may lead to the sign change of ${\cal
S}_3$
