We have obtained UBVRI and JK photometry and radial velocities for 13 field RR Lyrae stars with a large range of metallicity. Our sample includes eleven ab-type and two c-type variables. The surface brightness method is applied to these RR Lyrae stars to determine their mean absolute magnitudes <MV> as well as their distances and radii. We have used the Kurucz’s model atmospheres to provide metallicity- and gravity-dependent color-temperature transformations and bolometric corrections. Our results indicate a clear correlation between the luminosities of the RR Lyrae stars and their metallicities such that metal-poor RR Lyrae stars are more luminous.