BACKGROUND: Individual variations of the pharmacokinetics of recombinant human TSH (rhTSH) might influence the efficacy of the radioactive iodine (RAI) uptake. We studied to investigate the individual pharmacokinetics of rhTSH and the effect of the anthropometric parameters on the serum TSH levels in patients with thyroid papillary carcinoma. METHODS: We selected 16 patients with conventional rhTSH administration for the preparation of RAI administration between June 2004 and May 2005. We measured serum TSH levels at 24-hour (prior to second rhTSH injection), 48-hour (peak level, prior to RAI administration) and 96-hour (prior to scanning) after the first rhTSH injection. We analyzed the correlation of each TSH levels with age, height, weight, creatinine clearance, body mass index (BMI), and body surface area (BSA). RESULTS: Peak TSH levels were negatively correlated with weight, BMI, and BSA. Among them, weight was an independent parameter by multivariate analysis. Decrement of serum TSH levels from the peak to the level at 96-hour was negatively correlated with weight, BMI, and BSA. It was positively correlated with increment of serum TSH levels from the level at 24-hour to the peak level. Serum TSH level at 96-hour was lower than 25 mU/L in nine of 16 patients. CONCLUSION: Body weight was inversely correlated with peak TSH level after rhTSH administration. rhTSH-stimulated TSH levels might be exaggerated to unwanted levels, and very rapidly degraded in lower-weighted patients. We should make up for the rhTSH regimen considering the individual variations of its pharmacokinetics.