  We have discovered four AGN in the ROSAT all-sky-survey data with very steep
X-ray spectra. We apply several models to these X-ray spectra with emphasis on
warm absorber models which give an adequate description of the data. We report
on the follow-up optical and radio observations which allow the identification
of three of these objects as Narrow Line Seyfert 1 galaxies, and the fourth as
BL Lac object. We have measured small-FWHM Hbeta lines, strong FeII emission
and weak [OIII] emission in the three Narrow Line Seyfert 1 galaxies, in line
with known correlations with respect to the steepness of the X-ray spectra. We
have discovered strong optical variability in the BL Lac object and two of the
Seyfert galaxies using photographic plates of the Sonneberg Observatory field
patrol. We finally discuss the statistical implications of our search algorithm
on the expected number density of soft X-ray selected AGN and conclude that up
to 30% of X-ray selected AGN might have supersoft X-ray spectra.
