SummaryOBJECTIVEIGF‐I rises in normal adolescence and in central precocious puberty (CPP), secondary to a rise in sex steroids and GH. The aim of this study was to examine changes in serum IGF‐I and its major binding protein IGFBP‐3 after pharmacological arrest of puberty.PATIENTS AND MEASUREMENTSTen girls diagnosed for CPP were evaluated before and during the first 3 months of GnRH analogue (GnRHa) therapy aimed at Suppression of the gonadal axis. Serum IGF‐I was measured by immunoradiometric assay (IRMA) and IGFBP‐3 by both IRMA and Western ligand blotting (WLB).RESULTSSerum IGF‐I was markedly higher in patients with CPP as compared with age matched controls (48.8 ± 6.5vs23.1 ± 4.9 nmol/l,P<0.01). While GnRHa therapy caused serum oestradiol levels to return to pre‐pubertal levels in all 10 patients, serum IGF‐I levels decreased only minimally after 1, 2 or 3 months of therapy (43.2 ± 5.6, 42.3 ± 6.4 and 44.1 ± 7.2 nmol/l respectively). Serum IGFBP‐3 levels as determined using IRMA were also higher in CPP compared with age matched controls (4.70 ± 0.37vs3.71 ± 0.42mg/l,P<0.01). These differences were also evident when measured by WLB. GnRHa therapy caused a small and insignificant decrease in serum IGFBP‐3 levels after 1, 2 or 3 months of therapy (4.57 ± 0.33, 4.48 ± 0.4 and 4.42 ± 0.3 mg/l respectively).CONCLUSIONSThe lack of suppression of both IGF‐I and IGFBP‐3, despite therapy which halts puberty and slows growth velocity, suggests that steroids may be involved In the Induction of changes in the GH/IGF‐I axis but