Recent evidence suggests that GH and insulin growth factor-I (IGF-I) play a role in adrenal steroidogenesis. On the other hand, it has been shown that ACTH stimulates IGF-I secretion by cultured fasciculata adrenal cells. Aim of the present study was to investigate the influence of GH administration on adrenal steroids and IGF-I responsiveness to ACTH in children affected with isolated GH deficiency. Ten children (seven males and three females, 5-10 yr old) affected with isolated GH deficiency underwent a synthetic ACTH 1-17 test before and after administration of human recombinant GH at a dose of 4 IU/day sc for 10 days. After the therapy, no significant differences were detected in the responses of cortisol, dehydroepiandrosterone-sulfate, androstenedione, and 17-hydroxyprogesterone to ACTH 1-17, whereas an increased 11-deoxycortisol responsiveness to ACTH 1-17 was noted (P less than 0.005). Surprisingly, IGF-I significantly increased in response to ACTH 1-17 after short-term rGH administration (P less than 0.006). In conclusion, our data indicate that in isolated GH deficiency a short-term GH therapy does not substantially modify the adrenal responsiveness to exogenous ACTH, even if an increased 11-deoxycortisol and an induced IGF-I responsiveness to ACTH were observed.