  We present a new mapping algorithm, the "Accretion Stream Mapping (ASM)"
which uses the full phase-coverage of a light curve to derive spatially
resolved intensity distributions along the accretion stream in magnetic
cataclysmic variables of AM Herculis type (polars). The surface of the
accretion stream is approximated as a duodecadon shaped tube. After
successfully testing this method on artificial data we applied it to emission
line light curves of Hbeta, Hgamma and He II lambda 4686 of the bright
eclipsing polar HU Aqr. We find Hydrogen and Helium line emission bright in the
threading region of the stream where the stream couples onto magnetic field
lines. It is particularly interesting, that the stream is bright on the
irradiated side, facing the white dwarf, which highlights the interplay of
collisional and radiative excitation/ionization.
