The paper describes a new type of high-resolution XUV radiation source which is based upon spontaneous anti-Stokes scattering of tunable incident laser radiation from atoms excited to metastable levels. The theory of the source is summarized and two sets of experiments using He (1s2s)1S atoms, produced in a CW hollow cathode and in a pulsed high-power microwave discharge, are discussed. The radiation source is used to examine transitions originating from the 3p6shell of potassium. The observed features include four previously unreported absorption lines and several sharp interferences of closely spaced autoionizing lines. A source linewidth of about 1.9 cm-1at 185 000 cm-1is demonstrated.