  The analysis of metal-rich HII regions has a profound impact on the
calibration of abundance diagnostics widely used to measure the chemical
content of star-forming galaxies, both locally and at high redshift. I review
the main difficulties that affect direct abundance determinations from
temperature-sensitive collisionally excited lines, and briefly discuss
strong-line methods, in particular their empirical calibration. In the near
future it will be possible to calibrate strong-line methods using metal
recombination lines, providing abundances that are virtually insensitive to
uncertainties on the nebular temperature structure.
