In recent years, advances in genetic engineering and in several other fields have led to the development of many new pharmaceutically active polypeptides. Because many of these polypeptides have extremely short plasma half-lives and are not active orally, the development of new delivery routes of administration or new delivery systems capable of controlling the release of these materials in their active forms are of considerable interest. Controlled release products for parenteral applications, such as implants or microparticulate systems have gained increasing importance and appropriate delivery systems for peptides have become the subject of intensive research. Therefore, the therapeutic and commercial potential of these peptides will only be fully realized if these advances are accompanied by improvements in the design of dosage forms leading to practical and effective formulations. The intent of this review is to summarize the work done in the field of controlled and/or prolonged release systems for peptides from the hypothalamic pituitary axis and their analogs. The potential in controlled and/or prolonged peptide delivery and the particularity of various kind of controlled delivery systems are discussed.