[en] Metastable atom de-excitation spectroscopy (MDS) provides a powerful technique with which to investigate surface electronic structure with unparalleled surface specificity. A thermal energy beam of noble-gas metastable atoms is directed at the surface under study and the kinetic energy distribution of ejected electrons that result from metastable-atom de-excitation is measured. Although the measured distribution contains information about the electronic structure of the outermost surface layer, its detailed analysis requires knowledge of the dynamics of the metastable atom-surface interaction. These dynamics were investigated directly here, for the first time, by use of spin-labeling techniques. The electron spins on the incident metastable atoms are polarized, and the spin-polarization of the ejected electrons is measured with a Mott polarimeter. Results are reported for Cu(100) and Ni(111) surfaces under a variety of surface conditions. The data indicate that metastable atom-surface interactions may be more complex than is generally assumed, suggesting that assumptions inherent in earlier analyses of MDS spectra merit additional investigation. The work further demonstrates the power of spin-resolved measurements in study of particle-surface interactions and in surface spectroscopies in general