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Although an excellent review on the subject of peptide hormones has rather recently appeared i n this Review ( 1) and a number of other papers summarizing the subject have been published (2-6), research in the field of the melanocyte-stimulating and adrenocorticotropic hormones has pro­ gressed so quickly and has reached so critical a stage that the author feels justified in concentrating on just this portion of "nonsteroid hormones." The reader will also find, however, a number of allusions to angiotensin, a peptide which certainly can be regarded as a "tissue hormone," but which might also have hormonal functions in the classical sense (aldosterone release). The last year has seen the fructification of new synthetic methods de­ veloped by the author's group (7, 8) that are especially well suited for the . synthesis of large and complicated peptides. This work has resulted in the synthetic preparation of a-MSH, ,B-MSH, and even ACTH, and has made feasible the manufacture of large quantities of the corticotropically highly active {:Jl-24 -corticotropin, a peptide with 24 amino acid residues. Synthetic peptides are helping us to understand better the physiological and metabolic functions of hormones: the availability of synthetic angioten­ sin (9), for example, was of prime importance for the discovery of its elTect on the adrenals. Biological actions of the melanophore-stimulating hormones which might shed some light on their physiological significance are emerging. Especially interesting is the possibility of peptide hormones acting directly or indirectly on the genetic apparatus to stimulate protein and enzyme syn­ thesis. These and other problems (e.g., structure-function relationship) will be discussed in this review. Before proceeding, I must mention the suggestions put forward by the Fifth European Peptide Symposium for the nomenclature and abbreviation of amino acids and peptides (10). Three-letter symbols, fashioned mainly ac­ cording to the suggestions of Brand & Edsall ( 1 1), represent, when standing by themselves, the free amino acid. Introduction of a hyphen before the symbol indicates substitution for a hydrogen of the a-amino group: after the symbol, substitution i n place of the hydroxyl of the a-carboxyl group; and above or below the symbol, substitution of functional groups (amino and