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Growth hormone (GH) influences a range of physiological functions, including renal plasma flow and glomerular filtration rate. Cells that secrete GH comprise a relatively large percentage of the total population of pituitary cells. The secretory activity of these cells is primarily regulated via peptide neurohormones from the hypothalamus. Direct influences of certain other factors have also been described. Human GH is present as a heterogeneous mixture of at least 20 molecular forms, most of which are 22,000 or 20,000 molecular weight monomers. Following release from the pituitary gland, GH circulates in either a 'free' form or bound to GH binding proteins. These binding proteins may have important effects on GH clearance and GH action at the level of the target tissue. The effects of GH are mediated, to a large extent, by insulin-like growth factors, formerly known as 'somatomedins'. The secretory pattern of GH is episodic, and occurs in bursts of varying frequency, amplitude, and duration. Changes in the pattern of GH secretion and its control occur with age. Recent data suggest that the specific characteristics of GH secretory bursts in humans are important to normal growth during childhood and adolescence.