Abstract Acylated crude papain has been shown to exert stereoselective behavior toward racemic hydrazides devoid of an amino acid residue, namely, ( RS )-mandelic and ( RS )-atrolactic hydrazides. These hydrazides functioned as nucleophiles to yield N 1 , N 2 -diacylhydrazines. Several achiral acylating agents for the enzyme were chosen, including Z -glycine, BOC-glycine, AOC-glycine, and hippuric acid. With the exception of hippuric acid as the acylating agent, the reaction product, in every instance for these achiral hydrazides, consisted of an excess of the (+)- N 1 , N 2 -diacylhydrazine. The relative rates of product formation for the mandelic hydrazides were considerably greater than for corresponding reactions with racemic atrolactic hydrazide. When chiral Z - l -alanine was employed to acylate crude papain, the stereoselective action was most pronounced, with the formation of a mixture of diastereoisomers consisting of 73% N 1 -( Z - l -alanyl)- N 2 -[( R )-mandelyl]hydrazine. The relative reactivities for the electrophiles was Z - l -alanine ⋙ Z -glycine ⋍ hippuric acid ⪢ AOC-glycine > BOC-glycine. The hydrazides of ( R )-, ( S )-mandelic, and ( RS )-atrolactic acids were prepared by conversion of the corresponding acids to their esters by means of a catalytic dehydrating agent and subsequent treatment with a methanolic solution of hydrazine.