['An interaction between ghrelin, which is implicated in the regulation of short- and long-term energy balance, and thyroid function has been reported in hyperthyroidism in which ghrelin levels are reversibly suppressed. We measured serum ghrelin levels and metabolic indices in hypothyroid patients before and after L-thyroxine replacement.', 'Eleven patients were examined twice: 1) in the hypothyroid state and 2) after at least 2 months of euthyroidism. Ten healthy subjects served as a control group. Ghrelin was measured in conjunction with indirect calorimetry and a hyperinsulinemic euglycemic clamp.', 'Serum ghrelin levels were increased by 32% under basal conditions in the hypothyroid state (PRE) as compared with posttreatment (POST) (picograms per milliliter): 976.4 +/- 80.8 vs. 736.8 +/- 67.1 (P < 0.001). This difference prevailed during the clamp, but a decline was observed in both states: 641.4 +/- 82.2 vs. 444.3 +/- 66.8 microg/ml (P = 0.005). The hypothyroid state was associated with decreased resting energy expenditure, increased respiratory quotient, and insulin resistance. Serum ghrelin levels as well as the metabolic aberrations became normalized after L-thyroxine replacement as compared with the control subjects.'] Are serum ghrelin levels increased in hypothyroid patients and become normalized by L-thyroxine treatment?