It has been shown that growth hormone (GH) and insulin-like growth factor-1 (IGF1) enhance steroidogenesis responsiveness to ACTH in cultured adrenal cells. To investigate the GH effect on adrenal steroidogenesis in non-GH-deficient subjects, we studied 9 girls with Turner syndrome (chronological age 5.5-7.2 years; bone age 5-7 years). In all subjects an ACTH test (Synacthen depot, 0.25 mg i.v. with blood samples at 0 and 60 min) was performed basally at 8-9 a.m. and 6 months after GH therapy (1 IU/kg/week). 17-Hydroxypregnenolone (17PGN), 17-hydroxyprogesterone (17OHP), dehydroepiandrosterone (DHA), its sulfate (DHA-S), androstenedione and cortisol were evaluated by radioimmunoassay. Two groups of normal girls were selected as controls: group A age-matched the patients at the start of the study, and group B age-matched the patients at the end of the study. The responsiveness of each hormone to ACTH was expressed as the difference between stimulated and basal values. A p value of < 0.01 was considered to indicate significance. There were no significant differences between pre- and posttreatment basal values of 17PGN, 17OHP, DHA, androstenedione and cortisol in the Turner syndrome patients, whereas a significant increase was observed for basal DHA-S (1.57+/-0.31; 1.89+/-0.43 micromol/l, p < 0.01). Comparison of increments before and after GH treatment showed a significant increase in responsiveness to ACTH after GH therapy DHA (p < 0.01). The increase in 17PGN was evident (p < 0.02), but the established significant p value was not reached. No differences for 17OHP, androstenedione and cortisol were found. The stimulated 17PGN/17OHP ratio was significantly higher (p < 0.01) after GH, whereas the 17OHP/androstenedione ratio was considerably lower, but the p value was < 0.02. No differences between pretreatment values with the control group androstenedione was found, whereas basal and stimulated posttreatment values of DHA and stimulated values of 17PGN were higher in patients after GH therapy than in control group B. No differences between the 2 control groups were found. In conclusion our study showed that adrenal steroid responsiveness to ACTH increases in Turner syndrome after long-term treatment with high GH doses. An increase in the number of ACTH adrenal receptors and/or a modulation of enzyme activities may be suggested. The positive or negative pharmacological implications of these data remain to be determined especially when taking into consideration the wide use of GH therapy in non-GH-deficient subjects.