Reduction of a double bond at C-1 of 1,4-dien-3-one steroids 7 and 8 with LiAl²H₄ in THF or NaB²H₄ in MeOH and H₂O gave stereospecifically [1α-²H]-labeled 4-en-3-one steroids 9 and 10, respectively. When the deuterated solvents, MeO²H and ²H₂O, were used for the reaction of steroid 8 with NaB²H₄, [1α,2ξ-²H₂]-labeled compound 10 was produced. This indicates that the reaction proceeds through the initial hydride attack at the C-1α position, followed by ketonization of the 2-en-3-ol intermediate.