We present a LTE model atmosphere analysis of the EUVE medium and long wavelength spectrum of the cool DO white dwarf HD 149499 B .
This observation in the spectral range 230-700 Å supplements a previous analysis of an ORFEUS spectrum between 912 and 1170 Å which yielded the atmospheric parameters T _ { eff } = 49500 \pm 500 K and \log g = 7.97 \pm 0.08 and a hydrogen-to-helium number ratio of 0.22 \pm 0.11 .
The EUVE data are in full agreement with the ORFEUS result and allow a more precise determination of the effective temperature ( T _ { eff } = 49500 \pm 200 K ) and the interstellar hydrogen column density ( N _ { H } = 7 \cdot 10 ^ { 18 } cm ^ { -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 .