  We present new results from our spectral analyses of very hot central stars
achieved since the last IAU Symposium on planetary nebulae held in Canberra
2001. The analyses are mainly based on UV and far-UV spectroscopy performed
with the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer
but also on ground-based observations performed at the Very Large Telescope and
other observatories. We report on temperature, gravity, and abundance
determinations for the CNO elements of hydrogen-rich central stars. In many
hydrogen-deficient central stars (spectral type PG1159) we discovered
particular neon and fluorine lines, which are observed for the very first time
in any astrophysical object. Their analysis strongly confirms the idea that
these stars exhibit intershell matter as a consequence of a late helium-shell
flash.
