  The experiments sensitive to pp-neutrinos from the Sun are very perspective
for the precise measurement of a mixing angle $\theta_{12}$. A $\nu $e$^{-}$
scattering experiment (Xmass) and/or a charged-current experiment (the indium
detector) can measure the flux of electron pp-neutrinos. One can find the total
flux of pp-neutrinos from a luminosity constraint after the contribution of
$^7$Be and CNO neutrinos to the total luminosity of the Sun are measured. The
radiochemical experiment utilizing a lithium target has the high sensitivity to
the CNO neutrinos, thus, it has a good promise for the precise measurement of a
mixing angle and for the test of a current theory of the evolution of the
stars.
