A new method for the determination of [Fe/H] in RR Lyrae stars.

The Fourier parameters of the V light curves of the field RRab stars are used to fit their [Fe/H]. The method is based on the assumption that the observed light curves depend only on a few physical parameters, including the chemical composition. We give two formulae which estimate the observed [Fe/H] with an accuracy of 0.23-0.18dex. Each of these expressions consists of a second order polynom of 2-4 Fourier parameters and the period. The method is a powerful tool in estimating the metallicity when spectroscopic data are not available.