While line blanketed, LTE Kurucz model atmospheres are widely employed
for early-type stars, the assumption of LTE breaks down for hot,
low gravity stars (see Fig. 2).
Considerable
effort has gone into developing realistic non-LTE model
atmospheres for early-type stars in recent years. Ideally, temperatures
are obtained using ionization equilibrium techniques, i.e.
from suitable diagnostic lines of adjacent ionization stages
showing a strong temperature dependence.
Naturally, determinations of 
from model atmospheres are
critically dependent on assumptions going into those models
and the accuracy with which surface gravities and elemental abundance
ratios are
determined. Unfortunately, due to the complexity of consistently
treating metal line blanketing in extended atmospheres, i.e.
considering the influence of thousands to millions of spectral
lines on the atmospheric structure (via backwarming) and
emergent spectrum (via line blocking), various statistical
simplifications are employed (Hillier, these proc.)