  We consider viscosity solutions to nonlinear uniformly parabolic equations in
nondivergence form on a Riemannian manifold $M$, with the sectional curvature
bounded from below by $-\kappa$ for $\kappa\geq 0$. In the elliptic case, Wang
and Zhang \cite{WZ} recently extended the results of \cite{Ca} to nonlinear
elliptic equations in nondivergence form on such $M$, where they obtained the
Harnack inequality for classical solutions. We establish the Harnack inequality
for nonnegative {\it viscosity solutions} to nonlinear uniformly {\it parabolic
equations} in nondivergence form on $M$.
  The Harnack inequality of nonnegative viscosity solutions to the elliptic
equations is also proved.
