We have treated five GH-deficient prepubertal children (4 M, 1 F) with GH releasing hormone 1-40 (GHRH1-40) in two dosage regimens over 9 months. Profiles of serum GH concentrations were obtained over 24 hours before treatment and nocturnal profiles were obtained serially throughout the study. GHRH was administered subcutaneously at night for four pulses using 1 microgram/kg/pulse in the first 3 months and 2 micrograms/kg/pulse for a further 6 months. All subjects demonstrated pituitary responsiveness to i.v. GHRH before treatment and at 3 and 6 months. GH secretion was induced in a pulsatile fashion in response to subcutaneous GHRH in three children from the first night of treatment. A self priming effect to successive GHRH pulses was evident and the response augmented with time and with the higher dose regimen. The growth velocity of these three children increased from a mean of 3.7 cm/year (range 3.7-3.8) before treatment to 5.5 cm/year (range 4.1-7.2) over the first 3 months and to 7.2 cm/year (range 4.8-9.2) over the following 6 months. In one subject entrainment of GH secretion to GHRH did not occur until the higher dose regimen and this was associated with a modest increase in growth velocity. One subject did not respond to treatment. Pulsatile administration of GHRH1-40 is effective in inducing GH secretion and promoting growth acceleration in some children with idiopathic GH deficiency. The optimal dose and mode of administration of GHRH have yet to be established.