[en] Absorption spectra of Moessbauer ¹⁸¹Tasup(*)(W) radiation in tantalum have been measured with the source placed in a static magnetic field H₀ approx. 3400 Oe with a rf magnetic field resonant with respect to the frequency of the excited state 3 MHz with amplitudes of 300 and 360 Oe, a rf field of 4 MHz with an amplitude of 300 Oe and without rf field. The dramatic change of the spectrum in the resonant field of 300 and 360 Oe, consistent with the theoretical prediction, is evidence for the observation of the NMR Moessbauer double resonance. (orig.)