The present concept of growth hormone is not that of an isolated hormone. Growth hormone is closely related to all other parts of system. Chemically, it belongs of to a family of 3 hormones, with prolactin and human placental lactogen. This chemical relationship produces some similar effects. Physiologically, it belongs to a series of hormonal secretions of which the elements are gradually recognized. Above, it is under the control of a releasing factor, still not identified : somatostatin which is an inhibiting factor, tetradecapeptide recently isolated ; below, the majority of the totality of its actions are developped through another hormone, or group of hormones : somatomedine. Present work on this endocrine system suggests new therapeutic prospects.