  It is shown that the high-Delta m^2 part of the large mixing angle MSW
solution of the solar neutrino problem is disfavored by the Super-Kamiokande
data for low-energy upward-going events. A quantitative bound is obtained in
the three-neutrino scheme with a negligibly small element U_{e3} of the
neutrino mixing matrix, as indicated by the result of the CHOOZ long-baseline
antinu_e->antinu_e oscillation experiment.
