  We report first results of our systematic investigation of the magnetic field
structure of rotating single magnetic white dwarfs and of white dwarfs in
magnetic cataclysmic variables. The global magnetic field distributions on the
isolated white dwarf HE1045-0908 and the accreting white dwarfs in EF Eri and
CP Tuc have been derived from phase-resolved flux and polarization spectra
obtained with FORS1 at the ESO VLT using the systematic method of Zeeman
tomography.
