Steroidal dehydroamino acid methyl esters (methyl a-acetamino+( cholesta-3,5-dien-3-yl)acrylate ( l), methyl a-acetamino-p( pregna-3,5-dien-3-yl)acrylate (2), methyl cY-acetamino-p-( 3-methoxy-estra-1,3,5,( ),16-tetraene-17-yl)acrylate( ), methyl cY-acetamino-/3-(3/3-acetoxy-androsta-16-en-17-yl)acrylate ( ), methyl a-acetamino-p-( 3@benzoyloxy-androsta-16en-17-yl)acrylate ( ) ) have been hydrogenated to the corresponding a-amino acid methyl esters in the presence of rhodiumphosphine in situ catalysts. The hydrogenation is highly chemoselective in case of 3,5-dienes. Reduction takes place exclusively in the side-chain. On the other hand, both olefinic double bonds were saturated when the 17-( methyl acetamidoacrylate) moiety was bonded to steroids possessing A 16. Although the diastereoselectivity of hydrogenation is mainly determined by the steroid skeleton itself in the case of substrates possessing the acetamidoacrylate moiety in position-17, the ratio of epimers can be modified by the structure of the tertiary phosphine ligand varied systematically in rhodium-phosphine in situ catalysts. The highest diastereoselectivity (75/25) was obtained when estra-1,3,5-triene derivative was used as substrate in the presence of achiral rhodium-triphenylphosphine catalyst. The stereochemistry of hydrogenation resulting in new stereogenic centers is discussed on the base of NMR investigations.