The present invention relates to a novel process for obtaining (1S,4S)N-methyl-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-1-naphthaleneamine from a mixture of its isomers. The process involves isomerising the 1-position and the 4-position and effecting separation of the desired isomer by methods such as fractured crystallization. The process can be operated as a continuous process.