  We study the possibility of intrinsic (non-perturbative) charm in parton
distribution functions (PDF) of the proton, within the context of the CT10
next-to-next-to-leading order (NNLO) global analysis. Three models for the
intrinsic charm (IC) quark content are compared: (i) $\hat{c}(x) = 0$ (zero-IC
model); (ii) $\hat{c}(x)$ is parametrized by a valence-like parton distribution
(BHPS model); (iii) $\hat{c}(x)$ is parametrized by a sea-like parton
distribution (SEA model). In these models, the intrinsic charm content,
$\hat{c}(x)$, is included in the charm PDF at the matching scale $Q_c=m_c=1.3$
GeV. The best fits to data are constructed and compared. Correlations between
the value of $m_c$ and the amount of IC are also considered.
