We have obtained new spectrophotometric data for 28 H ii regions in the spiral galaxy NGC 300 , a member of the nearby Sculptor Group .
The detection of several auroral lines , including [ O iii ] \lambda 4363 , [ S iii ] \lambda 6312 and [ N ii ] \lambda 5755 , has allowed us to measure electron temperatures and direct chemical abundances for the whole sample .
We determine for the first time in this galaxy a radial gas-phase oxygen abundance gradient based solely on auroral lines , and obtain the following least-square solution : 12 + log ( O/H ) = 8.57 ~ { } ( \pm 0.02 ) -0.41 ~ { } ( \pm 0.03 ) ~ { } R / R _ { 25 } , where the galactocentric distance is expressed in terms of the isophotal radius R _ { 25 } .
The characteristic oxygen abundance , measured at 0.4 \times R _ { 25 } , is 12 + log ( O/H ) = 8.41 .
The gradient corresponds to -0.077 \pm 0.006 dex kpc ^ { -1 } , and agrees very well with the galactocentric trend in metallicity obtained for 29 B and A supergiants in the same galaxy , -0.081 \pm 0.011 dex kpc ^ { -1 } .
The intercept of the regression for the nebular data virtually coincides with the intercept obtained from the stellar data , which is 8.59 ~ { } ( \pm 0.05 ) .
This allows little room for depletion of nebular oxygen onto dust grains , although in this kind of comparison we are somewhat limited by systematic uncertainties , such as those related to the atomic parameters used to derive the chemical compositions .

We discuss the implications of our result with regard to strong-line abundance indicators commonly used to estimate the chemical compositions of star-forming galaxies , such as R _ { 23 } .
By applying a few popular calibrations of these indices based on grids of photoionization models on the NGC 300 H ii region fluxes we find metallicities that are higher by 0.3 dex ( a factor of two ) or more relative to our nebular ( T _ { e } -based ) and stellar ones .

We detect Wolf-Rayet stellar emission features in \sim 1/3 of our H ii region spectra , and find that in one of the nebulae hosting these hot stars the ionizing field has a particularly hard spectrum , as gauged by the ‘ softness ’ parameter \eta = ( O ^ { + } /O ^ { + + } ) / ( S ^ { + } /S ^ { + + } ) .
We suggest that this is related to the presence of an early WN star .
By considering a larger sample of extragalactic H ii regions we confirm , using direct abundance measurements , previous findings of a metallicity dependence of \eta , in the sense that softer stellar continua are found at high metallicity .