1.A study was made of the NMR spectra of 10 pairs of C-20 epimeric 17,20-dihydroxy compounds of the pregnane and isopregnane series.2.In all cases the spectra of the 20α- and 20β-epimers are quite different, either in the position of the signal of the angular 18-CH3group, or by the appearance of the spectrum from the protons at the C-20 and C-21 centers.3.In all cases, for a correct determination of the structure it is necessary to make a careful analysis of the stereochemical models of the studied compound