The role of Clinical Pathology Laboratory in normal and altered growth hormone secretion is discussed. In particular, it is reported that the normal GH secretion can be studied by serum and urine GH determinations whereas the diagnosis of GH deficiency rests upon the demonstration of an inadequate rise serum GH after provocative stimuli and serum measurement of somatomedins (IGF-I) by radioimmunoassay method. As it concerns increase GH secretion the diagnosis is clinically made (acromegaly and gigantism) and the laboratory has only the role to confirm it by the assessment of basal and stimulated GH secretion.