  For many years various asymmetrical profiles of different spectral lines
emitted from solar flares have been frequently observed. These asymmetries or
line shifts are caused predominantly by vertical mass motions in flaring layers
and they provide a good diagnostics for plasma flows during solar flares. There
are many controversial results of observations and theoretical analysis of
plasma flows in solar chromospheric flares. The main difficulty is the
interpretation of line shifts or asymmetries. For many years, methods based on
bisector techniques were used but they give a reliable results only for some
specific conditions and in most cases cannot be applied. The most promising
approach is to use the non-LTE techniques applied for flaring atmosphere. The
calculation of synthetic line profiles is performed with the radiative transfer
techniques and the assumed physical conditions correspond to flaring
atmosphere. I will present an overview of different observations and
interpretations of line asymmetries in chromospheric flares. I will explain
what we have learnt about the chromospheric evaporation in the frame of
hydrodynamical models as well as reconnection models. A critical review will be
done on the classical methods used to derive Doppler-shifts for optically thick
chomospheric lines. In particular, details on the new approach for interpreting
chromospheric line asymmetries based on the non-LTE techniques will be
presented.
