The secretion of hGH after the administration of the analogue of growth hormone releasing hormone, GHRH (1-29)NH2, to 8 normal adults and 41 short children has been studied. The children were classified on the basis of their hGH response to insulin-induced hypoglycaemia; 28 had severe hGH deficiency (peak serum hGH less than 7 mIU/litre) and 13 had simple short stature (peak serum hGH greater than 15 mIU/litre). The hGH response to GHRH was similar in normal adults and short stature children, but significantly lower in the hGH deficient children. In 23 (82%) of the hGH deficient children the peak serum hGH in response to GHRH was greater than 7 mIU/litre (the maximum value seen during hypoglycaemia), and in 14 (50%) the peak serum hGH in response to GHRH was greater than 15 mIU/litre. This suggests that in the majority of hGH deficient children the defect in hGH secretion results from hypothalamic GHRH deficiency. The hGH responses of the short stature children to insulin-induced hypoglycaemia were mainly in the low range of normal, and the majority showed normal hGH responses to GHRH. Eighteen prepubertal children with definite hGH deficiency have been treated for 3-18 months with twice daily, subcutaneous injections of GHRH. This has promoted linear growth in 12 children, of whom 8 showed an increment in height velocity of 2-11 cm/year. GHRH provides a valuable method for the assessment of hGH secretion, but by itself it cannot be used to establish deficient hGH secretion; this requires a stimulation test that promotes hypothalamic GHRH secretion, such as insulin-induced hypoglycaemia. GHRH is a practical alternative therapy to hGH for some hGH-deficient children.