Abstract: A novel compound--ethyl 6-bromo-5-hydroxy-4-dimethylaminomethyl-1-methyl-2-phenylthiomethylindole- 3- carboxylate hydrochloride monohydrate having the following formula: ##STR1## A process for preparing the compound according to the invention, characterized in that it comprises treating ethyl 5-acetoxy-1,2-dimethylindole-3-carboxylate with a brominating agent in an inert organic solvent under reflux, reacting the resultant ethyl 5-acetoxy-6-bromo-2-bromomethyl-1-methylindole-3-carboxylate with thiophenol in the presence of an alkali metal hydroxide or its alcoholate in an organic solvent, reacting the resultant ethyl 6-bromo-5-hydroxy-1-methyl-2-phenylthiomethylindole-3-carboxylate with an aminomethylating agent in an organic solvent at a temperature of from 65.degree. C. to a temperature of refluxing the reaction mixture. The end product is then isolated from the resultant base--ethyl 6-bromo-5-hydroxy-4-dimethylaminomethyl-1-methyl-2-phenylthiomethylindole- 3- carboxylate.