  We present new empirical and theoretical calibrations of two photometric
metallicity indices based on Walraven photometry. The empirical calibration
relies on a sample of 48 Cepheids for which iron abundances based on high
resolution spectra are available in the literature. They cover a broad range in
metal abundance (-0.5 < [Fe/H] < +0.5) and the intrinsic accuracy of the
Metallicity Index Color (MIC) relations is better than 0.2 dex. The theoretical
calibration relies on a homogeneous set of scaled-solar evolutionary tracks for
intermediate-mass stars and on pulsation predictions concerning the topology of
the instability strip. The metal content of the adopted evolutionary tracks
ranges from Z=0.001 to Z=0.03 and the intrinsic accuracy of the MIC relations
is better than 0.1 dex.
