  We obtained nebular spectroscopy of LMC HII regions having classified stellar
populations, thereby strongly constraining the ionization input parameters.
Using photoionization models, we then evaluate the performance of nebular
diagnostics of T_* and abundance. We introduce [Ne III]/H-beta as a nebular
diagnostic of the ionizing stellar T_*. In contrast to the widely-used
\eta-prime parameter, [Ne III]/H-beta has greater sensitivity to mid and early
O-stars, and is robust to nebular morphology and the presence of shocks. We
present a preliminary calibration of both T_* diagnostics for LMC metallicity.
We also introduce S234 = ([S II] + [S III] + [S IV])/H-beta as a diagnostic of
S abundance. S234 is much less sensitive to the nebular ionization parameter
than is S23 or R23. The intensity of [S IV]10.5 microns is easily estimated
from the optical and near-IR line ratios. We present calibrations of S23 and
S234 that are reliable at metallicities Z < 0.5 Z_sol.
