Résumé : Melanocytic naevi may grow more rapidly during human growth hormone (hGH) therapy. With standardised skin photographs, the growth rate of the naevi was two-fold greater in 14 hypopituitary and 5 Turner's syndrome girls treated with hGH than in untreated patients or controls. HMB-45 immunoreactivity, a marker of stimulated melanocytes, was absent in naevi from 18 of 19 individuals not treated with hGH, including 5 Turner's syndrome patients studied 2-43 months after stopping hGH. In naevi from 39 hGH-treated patients, 22 showed unusual HMB-45 reactivity in dermal naevocytes. During administration of hGH, melanocytic naevi grow faster and there is reversible stimulation of naevocytes.