A series of quaternary ammonium salts of 3-alkylaminoderivatives of 1,2,4-benzothiadiazine-1,1-dioxide were prepared and tested for cardiovascular activity. Almost all the substances tested proved to have some measure of depressant activity on arterial pressure and the most interesting compounds in this respect were (XII), (XIII), (XV) and (XIX) for which hypotensive values between 60 and 70% with respect to the base level were recorded. Compound (XV) also caused increase in the differential pressure and decrease of cardiac frequency. The later however was increased by some other compounds [(XII), (XVIII)]. The structure-activity relationships are discussed taking into account also the activity of the parent tertiary amines.