The key role of RR Lyrae stars as tracers of the oldest population (and therefore of the epoch of galaxy formation) in resolved Local Group galaxies has been confirmed by their discovery in several LG dwarfs. By comparing the properties of RR Lyr's in nearby galaxies with those of the Milky Way variables, the metallicity and age of the oldest population can be estimated.
A search for RR Lyrae variables in the Local Group Galaxies (Leo I, NGC 6822, Phoenix, Fornax) in collaboration with Held, Saviane, Momany and Rizzi (Padova Obs.) and Poretti (Milano Obs.) is being carried out. Based on multicolour WFI@2.2m and FORS1@VLT time series photometry, RR Lyrae and anomalous Cepheids have been detected for the first time in Leo I (Held et al. 2001), and NGC 6822 (Clementini et al., in preparation), thus providing unambiguous evidence for the presence of old metal-poor stars all the way to the innermost regions of these composite stellar systems, and opening the possibility to derive accurate distances to these galaxies via these primary distance indicators.
A deeper search for variables in Leo I, NGC 6822, Phoenix and Fornax is being carried out using the Optimal Image Subtraction Method package ISIS2.1 (Alard 2000).