The article reviews hormonally active peptides, mechanisms of their biosynthesis and chemical synthesis. Special attention is given to achievements of the Czech school of peptidology. Mechanisms of activity of peptidergic hormones is based mainly on the activation of adenylatcyclase and formation of the "second messenger", cAMP. Other three possible mechanisms are also reviewed. Main groups of peptidergic hormones (neurohypophyseal hormones, hypothalamic regulatory hormones, gastrointestinal hormones, natriuretic peptides, and many others) are described and their therapeutic and diagnostic significance is summarised. Future prospects of peptidology in the clinical praxis are briefly reviewed.