The technique of quantitative determination of L-thyroxin in a model solution and an individual preparation with the aid of inversion voltammetry is developed. For this purpose, it is necessary to study working conditions of the voltammetric behavior of L-thyroxin, namely, to estimate the influence of different factors (accumulation potential, accumulation time, scanning rate, nature of background electrolyte) on the potential and current of thyroxin recovery. The object of study is L-thyroxin (Sigma, USA). As a result, working characteristics of quantitative determination of L thyroxin in a model solution and monopreparation are determined.