The fluorescence development from amino acids andj epptides using N-chlorodansylamide (NCDA) is described. NCDA gave fluorecence on reaction with proline which gives no fluorescence with o-phthaladehyde (OPTA) or with fluorescamine. NCDA showed excellent sensitivity in the assay of peptides which give only poor fluroescene on reaction with OPTA. The standard curves for amino acids and peptides were linear in the range from 10 nmol to 100 nmol/sample and passed through the origin.