Abstract: The medicinal product comprises as active principle a melarsomine hydrochloride preparation having a purity of between 98.5 and 100%. The process for obtaining this preparation is stated essentially as follows:step 1, trichlorotriazine (TCT) is converted to diaminochlorotriazine (DCT) in an ammoniacal medium;step 2, the DCT is converted to melarsen acid hydrochloride (MAH) in the presence of arsanilic acid;step 3, the MAH is reduced to melarsen oxide dihydrate; andstep 4, the melarsen oxide dihydrate is converted to melarsomine dihydrochloride in the presence of cysteamine hydrochloride. In each step, a purified preparation of the corresponding intermediate product, or final product in step 4, is obtained.