  We perform a full next-to-leading analysis of the the available experimental
data on the polarized structure function g_1 of the nucleon, and give a precise
determination of its singlet axial charge together with a thorough assessment
of the theoretical uncertainties. We find that the data are now sufficient to
separately determine first moments of the polarized quark and gluon
distributions, and show in particular that the gluon contribution is large and
positive.
