A bioequivalence study between a new Levothyroxine solution and a reference solution was performed in 12 healthy volunteers after one single 3000 g oral administration. Administrations were done according to a cross-over schedule with a three week wash-out period. Plasma profile of Levothyroxine was determined for 72 hours, clinical tolerance being appreciated for 10 days after each administration. No statistical difference was reported for pharmacokinetic parameters and clinical tolerance was good.