Using pharmacological tests or GH profiles, GH deficiency or active acromegaly can be diagnosed. However, it is impossible to discriminate within the continuum between ‘deficiency/insufficiency’ and ‘sufficient secretion’. The use of GH to improve growth velocity is based on 1 injection once a day. It is thus the total amount of GH which appears to be important for its growth-promoting effect. An assay of GH in urine allows to assess such GH ‘production’, even over a prolonged period of time. A radiometric two-step assay applicable to untreated urine is presented. Results for assessing the ‘GH status’ by measuring GH in 24-hour urine, first morning-void urine or timed urine samples are shown. The correlation between 24-hour plasma profiles and the simultaneously collected 24-hour urine is significant at p < 0.01. A correlation coefficient > 0.9 was found between timed urine samples (4 h) and the 120-min plasma GH values during GHRH stimulation tests. The night-to-night variation of urinary GH can be very important. It is advisable, therefore, to use the mean of several night urines. The correlation between the mean urinary GH of 5 nights to one 24-hour sample is significant at p < 0.01. An age-dependent increase in urinary GH is found in the pubertal age group. The percentile distribution of 24-hour and night urines for the age groups < 7 years, prepuberty and puberty is given (P<sub>50</sub> GH in ng/night, mean of 3 urines: < 7 years = 0.49, prepubertal = 0.75, pubertal = 1.3). The respective 24-hour excretions are: < 7 years = 1.59, prepubertal = 2.62, and pubertal = 4.1 ng/24h Testosterone treatment of delayed puberty dramatically increases endogenous GH production, as shown by the urinary output. The high GH dose used to treat girls with Turner’s syndrome is reflected in a urinary output which is very similar to that found in boys on testosterone treatment. No correlation could be found between the GH dose used as supplementary treatment and urinary output. Furthermore, during GH therapy, the intraindividual excretion varies largely. It is concluded that urinary GH reflects the circulating GH, timed samples show the corresponding plasma values, the mean of several night (first morning-void) urines is a useful tool for assessing the GH status. Although pulsatility is obviously not reflected in urine, the varying total amount of GH secreted is modulated by pulse amplitude, and this is reflected indirectly in urinary GH. Urinary GH can be used to monitor GH therapy or any therapy intended to impair or increase endogenous GH production.