  Our analysis of the Deep CFHT M33 variability survey database has uncovered 5
Beat Cepheids (BCs) that are pulsating in the fundamental and first overtone
modes. With {\it only} the help of stellar pulsation theory and of
mass--luminosity (M-L) relations, derived from evolutionary tracks, we can
accurately determine the metallicities Z of these stars. The [O/H] metallicity
gradient of -0.16 dex/kpc that is inferred from the M33 galacto-centric
distances of these Cepheids and from their 'pulsation' metallicities is in
excellent agreement with the standard spectroscopic metallicity gradients that
are determined from H II regions, early B supergiant stars and planetary
nebulae. Beat Cepheids can thus provide an additional, independent probe of
galactic metallicity distributions.
