  We discuss the spin excitations in systems with hopping electron conduction
and strong position disorder. We focus on the problem in a strong magnetic
field when the spin Hamiltonian can be reduced to the effective single-particle
Hamiltonian and treated with conventional numerical technics. It is shown that
in a 3D system with Heisenberg exchange interaction the spin excitations have a
delocalized part of the spectrum even in the limit of strong disorder, thus
leading to the possibility of the coherent spin transport. The spin transport
provided by the delocalized excitations can be described by a diffusion
coefficient. Non-homogenous magnetic fields lead to the Anderson localization
of spin excitations while anisotropy of the exchange interaction results in the
Lifshitz localization of excitations. We discuss the possible effect of the
additional exchange-driven spin diffusion on the organic spin-valve devices.
