Alanine : glyoxylate, glycine : 2-oxoglutarate (EC 2.6.1.4), and serine : glyoxylate aminotransferases were isolated and partially purified by two different procedures from oat leaves (Avena sativa L. var. Garry). Initial velocity, enzyme resolution and reconstitution, pyridoxal 5-phosphate activation, and enzyme inhibitor studies showed that the serine : glyoxylate aminotransfer reaction operates by the Ping Pong Bi Bi mechanism and involves the coenzyme pyridoxal phosphate, as do other aminotransferases, but does not appear to involve metal ions or sulfhydryl groups. Enzyme specificity determinations suggested that glyoxylate aminotransfer reactions are catalyzed by protein(s) distinct from other aminotransferases. Results are discussed in relation to earlier work with comparable enzymes from wheat leaves and to similar studies with enzymes from animal sources.