  We have performed soft X-ray spectroscopy of two hot white dwarfs with the
Chandra observatory using the Low Energy Transmission Grating. The first target
is the hot DA white dwarf LB1919 (Teff=69000 K). This star is representative of
a small group of hot DAs whose metallicities lie well below predictions from
radiative levitation theory. The Chandra spectrum shows a rich absorption line
spectrum which may allow to find the origin of the low-metallicity nature of
these DAs. The second target is PG1520+525, a very hot non-pulsating PG1159
star. We find that it is hotter (Teff=150 000 K) than the pulsating prototype
PG1159-035 (Teff=140 000) and conclude that both stars confine the blue edge of
the GW Vir instability strip.
