  We note that the fine structure at the endpoint region of the beta decay
spectrum is now essentially known using neutrino oscillation data, if the mass
of one neutrino is specified. This may help to identify the effects of nonzero
neutrino masses in future experiments. An exact treatment of phase space
kinematics is used. This work is independent of theoretical models. Additional
restrictions due to the assumption of a so-called "complementary ansatz" for
the neutrino mass matrix are also discussed.
