We determined masses for the 7167 DA and 507 DB white dwarf stars classified as single and non-magnetic in data release four of the Sloan Digital Sky Survey ( SDSS ) .
We obtained revised T _ { \mathrm { eff } } and \log g determinations for the most massive stars by fitting the SDSS optical spectra with a synthetic spectra grid derived from model atmospheres extending to \log { g } = 10.0 .
We also calculate radii from evolutionary models and create volume-corrected mass distributions for our DA and DB samples .
The mean mass for the DA stars brighter than g=19 and hotter than T _ { \mathrm { eff } } = 12 000 K is \langle { \cal { M } } \rangle _ { \mathrm { DA } } \simeq 0.593 \pm 0.016 ~ { } { \cal { M } } _ { \odot } .
For the 150 DBs brighter than g=19 and hotter than T _ { \mathrm { eff } } = 16 000 K , we find \langle { \cal { M } } \rangle _ { \mathrm { DB } } = 0.711 \pm 0.009 { \cal { M } } _ { \odot } .
It appears the mean mass for DB white dwarf stars may be significantly larger than that for DAs .
We also report the highest mass white dwarf stars ever found , up to 1.33 ~ { } { \cal { M } } _ { \odot } .