A simple, sensitive and specific assay method was developed for the assay of sodium liothyronine (T3Na) from tablets. Sodium liothyrorn'ne was extracted from powdered tablets with a solvent system consisting of butanol and dilute hydrochloric acid. The solvent was removed under vacuum and the residue was dissolved in ammonical methanol. An aliquot of this solution was injected on a μBondapak C18column and the elution was carried out with a mobile phase consisting of methanol:water:phosphoric acid (55:45: 0.1). The effluent was monitored by U. V. detection at 254 nm. A linear calibration curve was obtained in the range of 10 to 250 ng on column with a precision of ±4% (C. V.). The internal standard consisted of 3, 3′, 5-triiodothyronine (T3′ or RT3). The usefulness of an alternate compound, 3, 5-diiodo-3′, 5′-dibromothyronine, which is not endogenous, was also demonstrated as an internal standard.