  The international project ``Microcalorimeter Arrays for a Rhenium
Experiment'' (MARE) aims at the direct and calorimetric measurement of the
electron neutrino mass with sub-electronvolt sensitivity. Calorimetric neutrino
mass experiments measure all the energy released in a beta decay except for the
energy carried away by the neutrino, therefore removing the most severe
systematic uncertainties which have plagued the traditional and, so far, more
sensitive spectrometers. Calorimetric measurements are best realized exploiting
the thermal detection technique. This approach uses thermal microcalorimeters
whose absorbers contain a low transition energy Q beta decaying isotope. To
date the two best options are 187Re and 163Ho. While the first beta decays, the
latter decays via electron capture, but both have a Q value around 2.5 keV. The
potential of using 187Re for a calorimetric neutrino mass experiment has been
already demonstrated. On the contrary, no calorimetric spectrum of 163Ho has
been so far measured with the precision required to set a useful limit on the
neutrino mass. In this talk we present the status and the perspectives of the
MARE project activities for the active isotope selection and the single channel
development. We also discuss the neutrino mass statistical sensitivity
achievable with both isotopes.
