Hormonal Proteins and Peptides: Corticotrophin (ACTH) is a collection of papers dealing with the chemistry and biology of adrenocorticotropic hormone (ACTH). One paper describes the structure-function studies made on ACTH, with reference to the steroidogenic activity of synthetic ACTH fragments and analogs. The paper also discusses the melanocyte-stimulating hormone (MSH) activity, as well as the behavioral effects among the extraadrenal properties of ACTH. Some problems related to ACTH receptors include the role of extracellular calcium and the characterization of ACTH receptors in fetal and adult human adrenocortical cells. Another paper describes ACTH synthesis in the pituitary and extrapituitary tissues. One paper analyzes the role of ACTH in the regulation process concerning the production of steroid hormones, particularly, on the generation of glucocorticoids. Glucocorticoids are the characteristic products of the zona fasciculata. Another paper shows that the steady-state level of ACTH synthesis and release are due to the effects of stimulatory factors such as CRF and inhibitory hormones (namely, the glucocorticoids on the corticotroph). The maintenance of responsiveness of ACTH-secreting cells (as a response to individual stress in humans) can be a manifestation of an inherent molecular characteristic. This collection will prove valuable to microbiologists, biotechnologists, and academicians connected with the biological sciences.