  Recent studies of precision electroweak observables have led to the
conclusion that a fourth generation is highly constrained. However, we point
out that a long-lived fourth generation can reopen a large portion of the
parameter space. In addition, it preserves baryon and lepton asymmetries
against sphaleron erasure even if $B-L=0$. It opens up the possibility of exact
$B-L$ symmetry and hence Dirac neutrinos. The fourth generation can be observed
at the LHC with unique signatures of long-lived particles in the near future.
