To investigate the influence of electronic properties of the tricyclic thiazine system on neuroleptic activity, a series of the isomeric N-dimethylaminopropylthienobenzothiazines was synthesized. All compounds were screened for neuroleptic activity in mice and rats. For the active compounds lowest active doses in the antiamphetamine test were determined. Activity appeared to be dependent on the mode of annelation of the thiophene molecule: compunds bearing the same substituent and side chain with the thiophene molecule in 2,3 and 3,4 annelation were active, while those compounds with a 3,2 annelation seemed to be devoid of activity at the given dose.