  We present preliminary results concerning the search for short-period
variable stars in Tucana and LGS3 based on very deep HST/ACS imaging. In the
one chip per galaxy we studied so far, a total of 230 and 80 candidates
variables were found, respectively. For Tucana, we identified 134 of them as RR
Lyrae stars (RRL) pulsating in the fundamental mode (RRab), 51 in the
first-overtone mode (RRc), and 37 in both modes simultaneoulsy (RRd), as well
as four candidate anomalous Cepheids (AC). In the case of LGS3, we found 45
RRab and 5 RRc, plus three candidates RRd and five candidate AC. The
metallicities obtained from the mean period of the RRab are [Fe/H]_{Tuc}=-1.7
and [Fe/H]_{LGS3}=-1.8.
