hGH has been used in the treatment of hGH deficient children for nearly 30 years. The optimum treatment regimen is, however, still unknown. Generally, administration has been by 2 or 3 intramuscular injections/week and the total weekly dose has been 0.3-0.5 IU/kg. Many factors are known to influence the effect of treatment, such as the dose and the age of the child. In animal studies, the optimum growth rate occurs when the physiological pulse frequency of growth hormone is simulated (i.e. intravenous infusions of growth hormone every 3 hours in the rat). In humans, optimal growth rates occur in children in whom the spontaneous secretion of hGH is associated with many peaks (pulses) of high amplitude. In hGH deficient children, growth rate increases when the weekly dose of hGH is administered daily rather than 2-3 times/week, thereby optimizing the body's utilization of the hormone. The hGH plasma profile after daily subcutaneous hGH injections is, however, different from the hGH plasma profiles of children growing normally, in whom hGH secretion is episodic with many sharp pulses during the day and night. Whether simulation of normal hGH plasma profiles will increase the growth rate in hGH deficient children and normalize their adult height requires further investigation.