We have analyzed the results of reactor and accelerator neutrino oscil
lation experiments in a model with mixing of three neutrino fields and
a neutrino mass hierarchy. It is shown that v(mu) reversible arrow v(
e) oscillations with 0.6 less than or equal to Delta m(2) less than or
equal to 100 eV(2) and amplitude larger than 2 x 10(-3) are not compa
tible with the existing limits on neutrino oscillations if the non-dia
gonal elements of the mixing matrix are small. Thus, if the excess of
positron events recently observed in the LSND experiment is due to (v)
over bar(mu) --> (v) over bar(e) oscillations, the mixing in the lept
on sector is basically different from the CKM mixing of quarks.