  New candidate variable stars have been identified in the Small Magellanic
Cloud cluster NGC121, by applying both the image subtraction technique (ISIS,
Alard 2000) and the Welch & Stetson (1993) detection method to HST WFPC2
archive and ACS proprietary images of the cluster. The new candidate variable
stars are located from the cluster's Main Sequence up to Red Giant Branch.
Twenty-seven of them fall on the cluster Horizontal Branch and are very likely
RR Lyrae stars. They include the few RR Lyrae stars already discussed by Walker
& Mack (1988). We also detected 20 Dwarf Cepheid candidates in the central
region of NGC121. Our results confirm the "true" globular cluster nature of
NGC121, a cluster that is at the young end of the Galactic globulars' age
range.
