In order to assess the value of urinary growth hormone (GH) as a reflection of central GH release, 42 prepubertal children with short stature and without organic disease were studied. A nocturnal GH profile and L-dopa and GH-releasing hormone (GHRH) tests were performed. Urinary GH was measured by means of a direct immunoradiometric method we have developed, using two monoclonal antibodies. Nocturnal urinary GH values correlated positively with plasma GH values expressed as the area under the curve (r = 0.76; p = 0.0001) or mean peak amplitude (r = 0.73; p = 0.0001). Also, urinary GH values correlated positively with peak plasma GH levels during the GHRH test (r = 0.64; p = 0.001). In contrast, no correlation was observed between peak plasma GH and urinary GH during the L-dopa test (r = 0.29; p = 0.11). This suggests a specific but as yet undetermined effect of L-dopa on urinary GH secretion.