  We investigate the possibility of a fourth sequential generation in the
lepton sector. Assuming neutrinos to be Majorana particles and starting from a
recent - albeit weak - evidence for a non-zero admixture of a fourth generation
neutrino from fits to weak lepton and meson decays we discuss constraints from
neutrinoless double beta decay, radiative lepton decay and like-sign dilepton
production at hadron colliders. Also an idea for fourth generation neutrino
mass model building is briefly outlined. Here we soften the large hierarchy of
the neutrino masses within an extradimensional model that locates each
generation on different lepton number violating branes without large
hierarchies.
