AbstractPolarized neutron scattering from clusters of polarized proton spins in solid material provides a new contrast variation method. Frozen solutions of apoferritin and of the large subunit of Escherichia coli ribosomes in a mixture of heavy water and deuterated glycerol have been studied at the conditions of dynamic nuclear spin polarization (H = 2.5 T, T< 1K, 4-mm microwave irradiation). The three basic scattering functions of contrast variation were derived by varying polarized neutron scattering with the polarization of target nuclei. They agree with results obtained from neutron scattering in H2O/D2O mixtures at room temperature. Furthermore, the proton spins appear to be polarized uniformly, at least to a structural resolution of 40Å. This is an important prerequisite for the in situ structure determination of macromolecular labels in larger host particles.