  We present a LTE model atmosphere analysis of the medium and long wavelength
spectrum of the cool DO white dwarf HD149499B. This observation in the spectral
range 230-700 A supplements a previous analysis of an ORFEUS spectrum between
912 and 1170 A which yielded the atmospheric parameters Teff=49500+-500 K and
log g = 7.97+-0.08 and a hydrogen-to-helium number ratio of 0.22+-0.11. The
EUVE data are in full agreement with the ORFEUS result and allow a more precise
determination of the effective temperature (Teff=49500+-200 K) and the
interstellar hydrogen column density (NH=7.E18cm^-2). None of the features in
the EUVE spectrum could be identified with any additional absorber besides
helium. Exploratory calculations with fully metal blanketed LTE model
atmospheres show that the metal abundances predicted by current diffusion
theory are clearly at variance with the observed spectrum.
