Various brands of over-the counter (OTC) exogenous thyroid hormones are available in health food stores and retail pharmacies. Two commercially available OTC thyroid products were analyzed for total thyroxine (T4) and triiodothyronine (T3) content. The strength of a liquid thyroid gland extract was unlabeled and that of the solid oral preparation was 45 mg per table. The T4 concentration of the liquid preparation was less than 10 micrograms/dL; that of T3 was below the analytical sensitivity of our assay (less than 15 ng/dL). Tablet content of T4 and of T3 was up to 0.5 micrograms and up to 50 ng, respectively. Preliminary data on these OTC thyroid gland extracts cannot be extrapolated to all OTC thyroid products, but they suggest that such products generally contain concentrations of T4 and T3 below clinical effectiveness. Further analytical study is warranted.