  We first discuss why there remains continuing, strong motivation to
investigate Hubble's Constant. Then we review new evidence from an
investigation of the Galactic Open Clusters containing Cepheids by Hoyle et al.
that the metallicity dependence of the Cepheid P-L relation is stronger than
expected. This result is supported by a new analysis of mainly HST Distance
Scale Key Project data which shows a correlation between host galaxy
metallicity and the rms scatter around the Cepheid P-L relation. If Cepheids do
have a significant metallicity dependence then an already existing scale error
for Tully-Fisher distances becomes worse and the distances of the Virgo and
Fornax clusters extend to more than 20Mpc, decreasing the value of H_0.
Finally, if the Cepheids have a metallicity dependence then so do Type Ia
Supernovae since the metallicity corrected Cepheid distances to eight galaxies
with SNIa now suggests that the SNIa peak luminosity is fainter in metal poor
galaxies. As well as having important implications for H_0, this would also
imply that the evidence for a non-zero cosmological constant from the SNIa
Hubble Diagram may be subject to corrections for metallicity which are as big
as the effects of cosmology.

Astrophysics