A new method for the preparation of allochenodeoxycholic and allocholic acids is described. The key steps in the synthesis are 1) simultaneous oxidation-dehydrogenation reaction of 3α-hydroxy 5β-bile acid formyl esters with iodoxybenzene catalyzed by benzeneseleninic anhydride, 2) reductive allomerization at C-5 of the 1, 4-dien-3-oxo hydroxy acids with lithium/liq. ammonia, and 3) subsequent reduction of the resulting 3-oxo 5α-compounds with K-Selectride.