There are several thousand published papers on biochemical testing of growth hormone status in children, an indication of the confused and inconclusive state of the subject. The size of the literature forced the restriction of the author’s intended systematic review to English-language papers published since 1974 (or later, for some parts of the review). Retrieval of papers via the British Medical Association library was limited by the considerable number of journal issues missing and by the copyright laws. In all, about 600 papers were acquired, including some from the King’s College School of Medicine library and the interlibrary loan system. The review is therefore far from complete. The evaluation of growth hormone (GH) status is complicated by many factors. Firstly, the secretion of GH is controlled by many general variables such as food intake, exercise, sleep and stress, and by factors such as age, body mass index, gender and pubertal stage. Secondly, the neuroendocrine control mechanisms are not yet fully elucidated. GH concentrations in blood are characterized by large pulses succeeded by very low levels, the largest pulses being seen during sleep. Thirdly, GH is not a single substance, there being the major 22 kDa species and a 20 kDa splice variant, and the extracellular domain of the tissue receptor appears in blood as a GH binding protein. The consensus of GH assays was and still is poor, and the effect of the GH binding protein on GH assays is poorly characterized. The de®nition of a short child is not simple. Although compiled from data on thousands of children, charts of height and height velocity versus age for normal children are least accurate at the extremes, where the numbers of subjects are low and the curve ®t poor. There is a need for regular reassessment to allow for secular trends, which at present would re ect greater adult height and earlier puberty. Prediction of adult height from mid-parental height is unreliable. Calculation of height velocity is inaccurate over periods of less than 6 months, as height velocity is not constant and errors of height measurement will contribute disproportionately. The third centile for height has commonly been used as the cut-off for short stature. A height velocity around the 25th centile is needed to maintain a position on the height centile chart. One of the major problems is that there is no `gold standard’ biochemical de®nition of growth hormone de®ciency (GHD) and only severe cases are recognizable clinically. Estimations of the 24-h or 12-h secretion rate from the area under the curve of plasma GH versus time have been largely invalidated by the insensitive immunoassays used. Continuous or intermittent sampling techniques are cumbersome and invasive procedures involving hospital admission, and the sampling frequency may introduce large errors. The same dif®culties have impeded the use of the plasma GH response to exercise or pulse amplitudeduring sleep. Estimation of 24-h, or more commonly overnight, urinary GH excretion requires very sensitive (immunometric) GH assays, which have been developed only recently.Moreover, urinary GH shows very high day-to-day variation. Provocation tests offered shorter and more controllable testing regimes, but until very recently data on normal children were lacking, for obvious ethical reasons. Various arbitrary cut-offs have been used, with little regard for the nature of the stimulant. These cut-offs were originally established to ration the meagre supplies of pituitary-derived GH for treatment and have changed with increasing availability of recombinant GH. Variable responses are found in all groups of subjects, and normal children Evidence-based Review Ann Clin Biochem 2001; 38: 1±2