  We present a series of systematic abundance measurements for a group of hot
DA white dwarfs in the temperature range 20,000-75,000K, based on far-UV
spectroscopy with STIS on HST, IUE and FUSE. Using our latest heavy element
blanketed non-LTE stellar atmosphere calculations we have addressed the heavy
element abundance patterns for the hottest stars for the first time, showing
that they are similar to objects like G191-B2B. The abundances observed in the
cooler (<50,000K) white dwarfs are something of a mystery. Some of the patterns
(e.g. REJ1032) can be explained by self-consistent levitation-diffusion
calculations but there is then a serious difficulty in understanding the
appearance of the apparently pure H atmospheres. We also report the detection
of photospheric HeII in the atmosphere of WD2218+706.
