  We argue that gravitational microlensing is a feasible technique for
measuring the mass function of brown dwarf stars in distant galaxies.
Microlensing surveys of the bulge of M31, and of M87 in the Virgo cluster, may
provide enough events to differentiate the behaviour of the mass function of
lenses below the hydrogen burning limit (though we find that M87 is a more
favourable target). Such objects may provide a significant supply of baryonic
dark matter, an interesting possibility for the study of galactic dynamics.
Furthermore, these systems have different metallicities than the solar
neighbourhood, which may affect the mass function. These considerations are
relevant in the context of star formation studies.
