D-Amino acids have been found to induce protoplast-like forms (crescents) inAlcaligenes fecalisstrain LB. This induction is similar in most respects to that by penicillin with the exception of the effects produced in tryptone.D-Amino acids appear to act synergistically with penicillin. The amino acid composition of cell walls ofD-amino acid and penicillin-induced crescents as well as of normal cells has been examined by column chromatography. The main difference between normal and crescent cell walls consists of a reduction in the amount of the basic peptide unit of the phenol-insoluble fraction. These results are discussed in relation to the induction of protoplast-like forms.