The two title compounds 3-methoxy-17-keto-17-benzyl-16,17-secoestra-1,3,5(10)-trien-16-nitrile, C₂₆H₂₉NO₂, (I) and (17S)-3-methoxy-17-hydroxy-17-benzyl-16,17-secoestra-1,3,5(10)-trien-16-nitrile, C₂₆H₃₁NO₂, (II), have similar conformations in the solid state. The models from molecular mechanics calculations show an improvement in the similarity of the calculated (modeled) structures. However, they also revealed that the global energy minimum structure of (I) is a structure with a rotated 17-benzyl moiety. Thus, the difference in the bio logical activity of the two compounds ((I) a moderate anti-oestrogen, (II) biologically inactive) must be primarily caused by the difference in the orientation of the 17-benzyl moiety in the free molecules. In (II), the molecules are linked by weak O—H…N hydrogen bonds, forming spirals along the b direction.