The paper shows that threshold photoelectron spectroscopy can be successfully performed, even if the spin polarization is the object of interest. Using circularly polarized radiation from the Bonn 2.5 GeV synchrotron photoelectrons from argon atoms produced directly at threshold have been analyzed with respect to their energy by means of a threshold electron spectrometer and with respect to their spin in order to test this combined method. The comparison of the experimental result with predictions of a RRPA-calculation shows quantitatively good agreement.