Growth hormone is an important regulator of metabolism; both acromegaly and GH therapy in GH-deficiency are associated with a tendency towards insulin-resistance and loss of adiposity. A possible mediator of these effects is the recently identified white adipose tissue (WAT)-derived factor resistin that has been shown to impair glucose tolerance and inhibit adipocyte differentiation. We found that WAT resistin gene expression was significantly suppressed in GH-deficient (SDR) rats compared with their Sprague-Dawley background strain. However, within 4 h of treatment of SDRs with a bolus of rhGH (1.5 mg/kg) there was a significant 150-170% increase in WAT resistin mRNA. Moreover, 24 h continuous infusion of recombinant human GH (1 mg/kg/day) caused marked increases in epididymal and subcutaneous WAT resistin of 720% and 950%, respectively, compared to controls. By 48 h of infusion these values had fallen to 510% and 330%. Infusion of porcine GH (1 mg/kg/day) had a similar inductive effect on WAT resistin mRNA. Our data demonstrate an unexpected marked, rapid and sustained up-regulation of resistin by GH. This may indicate a role for resistin in GH-dependent metabolic and differentiative effects in WAT.