Growth hormone releasing factor (GRF) is one of two main releasing hormones which control pituitary hGH production and release. This activity is retained even when the length of the GRF polypeptide is reduced to the 29 N-terminal residues. This 29-residue polypeptide has been chemically synthesized, and testing in healthy volunteers elicited secretion of hGH to a maximum level of about 40 ng/ml. In a trial of children with various disorders, the maximum hGH response was reached within 60 minutes; those children with hGH deficiency showed much lower responses than those with other disorders not related to hGH deficiency. The frequency of false-positive tests was low, and it is proposed that GRF testing could provide a useful additional tool in the diagnosis of hGH deficiency.