A retrospective analysis was made of 405 thyrotrophin-releasing hormone (TRH) stimulation tests on children who were successful applicants for growth hormone (GH) therapy in the UK between 1977 and 1981 inclusive. Thyroid-stimulating hormone (TSH) responses to TRH were divided into normal and those indicating pituitary or hypothalamic disease on the basis of criteria which eliminated variation in TSH assay between laboratories. Among children known to be hypothyroid 93% had abnormal TRH stimulation tests, but 35% of those children who were clinically euthyroid and who had normal serum thyroxin levels also had abnormal TSH responses to TRH. Abnormal TRH tests in the latter group were most common in euthyroid children who had GH deficiency with clearly defined aetiology and least common in those with idiopathic GH deficiency. Further work is required to clarify the interpretation of an abnormal TRH stimulation test in this group of children, but until this is done, such patients should be kept under regular review with respect to thyroid function.