Nocturnal urinary growth hormone levels in children with short and normal stature were measured by a sensitive enzyme immunoassay. Urinary GH excretion during sleep correlated positively with peak plasma GH values during pharmacological (r = 0.74, P less than 0.001) and sleep (r = 0.85, P less than 0.001) tests. The amounts of urinary GH excretion during sleep differed significantly from each other in the following groups: complete GH deficiency (mean +/- SEM: 0.1 +/- 0.1 ng/m2 of body surface area; range: less than 0.1-0.4), partial GH deficiency (1.6 +/- 0.3 ng/m2; 0.2-3.1), and short stature without GH deficiency (3.7 +/- 0.6 ng/m2; 0.7-11.5). No significant difference was found between short stature without GH deficiency and normal stature (5.0 +/- 0.5 ng/m2; 2.1-10.5). Measurement of nocturnal urinary GH excretion is a simple method for screening of GH excretion and may be helpful in the differentiation of the various etiologies of short stature in children.