To assess the clinical usefulness of urinary growth hormone (UGH) measurements, a UGH determination technique, including dialysis, ultrafiltration, and measurement by polyclonal-coated tube RIA, was established. Sixty-three short children were studied: 56 idiopathic growth retarded (37 prepubertal and 19 pubertal) and seven prepubertal with classic GH (growth hormone) deficiency. Forty-two healthy children (32 prepubertal and 10 pubertal) served as controls. Two groups of adults were studied: eight with active acromegaly and 11 healthy controls. UGH was measured in 24-h urine samples from all patients and controls. Mean ± SD UGH excretion expressed as ng/24 h was significantly lower in the GH-deficient group compared with prepubertal growth-retarded and control children (p < 0.01). No differences were found between UGH excreted by controls and by the growth-retarded groups. Pubertal children excreted significantly higher amounts of GH when UGH was expressed as ng/24 h (p < 0.02 and p < 0.03, respectively), but this difference disappeared when UGH was expressed as ng/g creatinine. UGH was significantly higher in acromegalic patients compared with adult controls (p < 0.001). Differences between day, night, and 24-h UGH were studied in 23 children. UGH in night urine was significantly lower whether expressed as the total amount or as ng/g creatinine. The effect of recombinant hGH administration on UGH was studied in 13 children after 6 and 12 mo of treatment. UGH increased significantly under recombinant hGH treatment. An endogenous GH secretion study was performed in 41 children: UGH expressed as ng/24 h correlated significantly with mean serum 24-h GH, IGF-I concentration, chronologic age, and growth velocity, whereas when expressed as ng/g creatinine, UGH correlated only with mean serum 24-h GH and growth velocity. In conclusion, UGH determination is a noninvasive, easily repeatable way of assessing GH secretion. UGH expressed as the total amount per 24 h would appear to be a more advantageous approach to the expression of UGH data for clinical purposes. © 1992 International Pediatric Research Foundation, Inc.