  We have carried out a re-analysis of polarimetric data of central stars of
planetary nebulae, hot subdwarfs, and white dwarfs taken with FORS1 (FOcal
Reducer and low dispersion Spectrograph) on the VLT (Very Large Telescope), and
added a large number of new observations in order to increase the sample. A
careful analysis of the observations using only one wavelength calibration for
the polarimetrically analysed spectra and for all positions of the retarder
plate of the spectrograph is crucial in order to avoid spurious signals. We
find that the previous detections of magnetic fields in subdwarfs and central
stars could not be confirmed while about 10% of the observed white dwarfs have
magnetic fields at the kilogauss level.
