  We present the first quantitative spectral analysis of blue supergiant stars
in the nearby galaxy NGC 2403. Out of a sample of 47 targets observed with the
LRIS spectrograph at the Keck I telescope we have extracted 16 B- and A-type
supergiants for which we have data of sufficient quality to carry out a
comparison with model spectra of evolved massive stars and infer the stellar
parameters. The radial metallicity gradient of NGC 2403 that we derive has a
slope of -0.14 (+/- 0.05) dex/r_e, and is in accordance with the analysis of H
II region oxygen abundances. We present evidence that the stellar metallicities
that we obtain in extragalactic systems in general agree with the nebular
abundances based on the analysis of the auroral lines, over more than one order
of magnitude in metallicity. Adopting the known relation between stellar
parameters and intrinsic luminosity we find a distance modulus m-M = 27.38 +/-
0.08 mag. While this can be brought into agreement with Cepheid-based
determinations, it is 0.14 mag short of the value measured from the tip of the
red giant branch. We update the mass-metallicity relation secured from chemical
abundance studies of stars in resolved star-forming galaxies.
