Regiospecific syntheses of the three monomethylthio analogues of 1-(2,4,5-trimethoxyphenyl)-2-aminopropane are described. The three isomeric amines were evaluated for potential psychotomimetic potency using the rabbit hyperthermia assay. Enantiomeric compositions and time-concentration curves in rat brains were determined following intraperitoneal administration of each compound. The biological data are contrasted with the corresponding results obtained with the potent human psychotogen 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM).