The synthesis of 25-hydroxycholesterol and 25-hydroxycholecalciferol from animal bile starting materials in which hyodeoxycholic acid or an ester thereof is converted to the 3.beta.-hydroxy-5-cholenic acid alkyl ester, and this is converted to 3.beta.-hydroxy-25-cyano-5-cholene by a series of steps by which the sterol nucleus is stabilized by placing a protecting group at the 3 position and then extending the chain from the carbon at the 24 position to a cyanide group at the 25 position. The compound so formed is subjected to a series of reactions by which it is transformed into 25-hydroxy-7-dehydrocholesterol which may then be irradiated with ultraviolet light to 25-hydroxycholecalciferol. The invention discloses new and improved processes for preparing these end products and also new compounds formed as intermediates and processes for preparing these intermediates.