The determination of methimazole was investigated by potentiometric titration in an alkaline medium involving its reaction with iodine and square wave voltammetry (SWV) in 0.1 mol/l Tris-HCl buffer at pH 7.2. In potentiometric titration, the range of determination was 10-500 micromol. A stoichiometric reaction was obtained within the concentration range 0.75-1.25 mol/l of sodium hydroxide by potentiometric titration. A linear calibration graph was obtained over the concentration range 1-700 micromol/l by SWV. The lowest concentration of methimazole detected was 0.5 micromol/l. The relative standard deviations (R.S.D.) were 0.81% in potentiometric titration and 2.89% in square wave voltammetric analysis of thyromazol tablets. The data showed that potentiometric titration using iodine in sodium hydroxide can be used for the determination of methimazole in drug samples without prior separation.