OBJECTIVE To evaluate serum thyrotropin (TSH) concentrations after conventional (0.9 mg) or half-dose (0.45 mg) administration of recombinant human TSH (rhTSH) injections intramuscularly in patients with end-stage renal disease and differentiated thyroid cancer. METHODS In this case series, we administered 2 doses of 0.9-mg rhTSH or 2 doses of 0.45-mg rhTSH to 3 patients with renal failure and differentiated thyroid cancer who were receiving hemodialysis. Basal serum TSH concentrations were assessed while the patients were taking thyroid hormone therapy. Serum TSH was measured on days 2, 3, 5, 8, 10, 14, and 17 of the study. Thyroglobulin and thyroglobulin antibodies were also measured on days 5 and 7. Patients were asked to report any adverse effects. RESULTS Patient 1, who received 2 injections of 0.9-mg rhTSH administered on days 1 and 3, had persistently elevated serum TSH levels for approximately 11 days. Peak serum TSH measured on day 5 was 644 mIU/L. Self-limited diarrhea was the only reported adverse effect. Patients 2 and 3 received 0.45 mg of rhTSH on 2 consecutive days (days 1 and 2), and both exhibited persistently elevated serum TSH levels for 12 days. The peak serum TSH values on day 3 were 402 mIU/L in Patient 2 and 386 mIU/L in Patient 3. No adverse events were observed in these 2 patients. Patient 2 received thyrotropin alfa for injection to confirm disease status. Patient 3 also received a radioiodine dose because of presumed persistent disease. CONCLUSION High serum TSH levels achieved after conventional and half-dose administration of rhTSH suggest that a dose adjustment might be considered in patients with end-stage renal disease.