Sunsnary: Reductive esterification occurs when unsaturated acids are treated with hydrogen in alcohol using either rhodium trichloride or the dimer of chloro(l$-hexadiene)rhodium(I) as the catalyst. Saturated acids containing appropriate functional groups are also esterified under the same conditions. Rhodium complexes are one of the most useful classes of catalysts for the homogeneous hydrogenation of unsaturated substrates.* Numerous publications have appeared, including ones concerned with the selective reduction of the double bond of olefins containing other functional groups located near the unsaturated moiety. For instance, treatment of a,B-unsaturated acids (e.g. p-methylcinnamic acid) with hydrogen and a catalytic amount of chlorotris(triphenylphosphine)rhodium(I) in benzene at 60' and 60-80 psi affords the corresponding saturated acids3. We now wish to report that a variety of unsaturated acids experience reductive esterification when subjected to hydrogenation in alcohol using a rhodium(I) or rhodium(II1) catalyst, and that certain unsaturated acids can also undergo esterification under the same conditions. When P-acetamidoacrylic acid (1) was treated with hydrogen and a catalytic quantity of chloro(l.5-hexadiene)rhodium(I) dimer in methanol, overnight at room temperature and one atmosphere, the saturated ester 2was formed in 96% yield. The ratio of substrate to catalyst ,NHCOCH3 [l,5-HDRhC1]2 CH =C-2 \ +H2 -CH3CHCOOCH3 COOH or RhC13 NHCOCH3 CH30H (I) (2) used was 25:l. Rhodium trichloride was equally effective as a catalyst for this reductive