['Turner syndrome (TS) is an indication for GH therapy in spite of the modest growth response. Somatic growth depends not only on GH insulin-like growth factor I (IGF-I) axis but also on thyroid hormone (TH) status. We have previously reported that supraphysiological IGF-I levels diminished TH actions in rat tissues by reducing the nuclear TH receptor (TR). GH treatment to TS patients induces high IGF-I levels and therefore a reduction of TH action in tissues may be expected. We aimed at evaluating the effect of GH therapy in TS girls on peripheral TH action.', 'We set up a reverse transcription-polymerase chain reaction (RT-PCR) for TR mRNA estimation in peripheral blood mononuclear cells (PBMC) and compared TR mRNA levels from 10 normal, 10 TS and 10 TS girls under GH therapy (0.33 mg/kg/week for 0.5-2 years).', 'After RNA extraction from PBMC, TR and beta-actin mRNAs were coamplified by RT-PCR. In addition serum biochemical markers of TH action were measured: thyrotropin (TSH), sex hormone binding globulin (SHBG), osteocalcin (OC), beta-crosslaps (beta-CL), iodothyronines by electrochemiluminescency and IGF-I by immunoradiometric assay (IRMA) with extraction.', 'TR mRNAs from PBMC were reduced in TS patients under GH treatment. In turn, serum TSH, OC, beta-CL and IGF-I were increased while SHBG was reduced by GH treatment in TS patients.'] Does growth hormone ( GH ) treatment reduce peripheral thyroid hormone action in girls with Turner syndrome?