  The microlensing surveys, such as OGLE or MACHO, have led to the discovery of
thousands of RR Lyrae stars in the Galactic Bulge and in the Magellanic Clouds,
allowing for detailed investigation of these stars, specially the still
mysterious Blazhko phenomenon. Higher incidence rate of Blazhko (BL) variables
in the more metal-rich Galactic Bulge than in the LMC, suggests that occurance
of Blazhko effect correlates with metallicity (Moskalik and Poretti 2003). To
investigate this problem, we calibrate the photometric method of determining
the metallicity of the RRab star (Kovacs and Zsoldos 1995) to the I-band and
apply it to the OGLE Galactic Bulge and LMC data. In both systems,
metallicities of non Blazhko and Blazhko variables are close to each other. The
LMC Blazhko pulsators prefer slightly lower metallicities. The different
metallicities of the Galactic Bulge and the LMC, can't explain the observed
incidence rates.
  As a by-product of our metallicity estimates, we investigate the
luminosity-metallicity relation, finding a steep dependence of the luminosity
on [Fe/H]
