  Analysis was performed of semi-inclusive and inclusive spin asymmetries
determined from the polarized deep inelastic scattering by the Spin Muon
Collaboration. Combined analysis of data for polarized deuterium and hydrogen
targets allows for separate determination of spin carried by valence {\it u}
and {\it d} quarks and non-strange sea quarks as a function of $x_{Bj}$ in the
range $0.006<x_{Bj}<0.6$. It was found that polarization of valence {\it u}
quarks is positive and of valence {\it d} quarks is negative, whereas the sea
polarization is small and consistent with zero within errors.
