Forty-six (46) eligible, healthy subjects who provide written informed consent will be enrolled to participate in a 2 arm parallel group study to assess and compare the pharmacokinetics and safety profile of Thyrogen dosed at 0.1 mg versus a modified release formulation of recombinant human thyroid stimulating hormone (rhTSH) dosed at 0.1 mg. Ten (10) of these subjects will have the thyroid uptake of radioiodine (123I) measured at baseline and following their single dose of study medication. All doses will be administered via intramuscular (IM) injection.