  A review of observational evidence in favour of a metallicity dependence of
WN and WC stars is presented. New near-IR studies of Milky Way, LMC and SMC
early-type WN stars are presented, with weake winds amongst WN stars containing
hydrogen. A metallicity dependence is supported for WN stars with hydrogen,
with dM/dt propto Z^alpha with alpha approx 0.8 +/- 0.2 The influence of CNO
content upon WN subtypes is discussed. Earlier WN spectral types are expected
(and observed) at lower metallicity due to the abundance sensitivity of NIII-IV
classification diagnostics. Recent physical and chemical results of WC stars in
the Milky Way and LMC are discussed, suggesting a metallicity dependence of
alpha approx 0.6 +/- 0.1. Earlier WC spectral types are predicted (and
observed) in lower metallicity galaxies, due to the dependence of the CIII
classification diagnostic on wind density. WO stars reveal lower wind
velocities at lower metallicity, whilst the situation for WN and WC stars is
unclear. Finally, the influence of a WR metallicity dependence upon the
ionizing flux distributions and optical line luminosities is addressed, with
particular regard to I Zw 18. Weaker winds at low metallicity would imply
harder ionizing flux distributions and lower line luminosities, arguing for an
substantially increased number of WR stars with respect to standard
calibrations, exacerbating difficulties with single star evolutionary models at
very low metallicity.
