Lysineless mutants ofSaccharomyces cerevisiaewere able to grow in liquid medium supplemented withL-lysine orDL-α-aminoadipic acid but not withD-α-aminoadipic acid.Nearospora crassastrain 33933, on the other hand, grew in the presence ofD-α-aminoadipic acid as the sole nutritional supplement. Growth was less efficient withD-α-aminoadipic acid than with theDL-form or withL- orDL-lysine, but the presence of a small amount of one of these latter compounds allowed maximal utilization of theD-α-aminoadipic acid. Acid-hydrolyzed cephalosporin C, but not untreated cephalosporin C, also served as a source of the nutritional requirement.