The invention concerns new sulfur-containing isoquinoline derivatives. More particularly, the invention relates to isoquinoline derivatives of the general formula (I) ##STR1## wherein R independently represents hydrogen, hydroxyl or alkoxy having 1 to 4 carbon atoms,R.sup.1 is hydrogen, alkyl having 1 to 4 carbon atoms and optionally substituted with phenyl, phenyl optionally substituted with one or more halogen or alkoxy group, cyano or carbamoyl,R.sup.2 is phenyl optionally substituted with one or more halogen, alkoxy or carboxyl, or a group of the general formula A ##STR2## wherein R.sup.3 is hydrogen, a straight or branched chained alkyl having 1 to 4 carbon atoms or phenyl,m and n independently represent 0, 1 or 2, with the proviso that m+n is at least 1,R.sup.4 is hydrogen, phenyl, hydroxyl, acyloxy, carboxyl, alkoxycarbonyl having 1 to 6 carbon atoms, carbamoyl, carbazoyl or dialkylamino containing 1 to 6 carbon atoms in the alkyl moiety, orR.sup.2 is a straight or branched chained alkylene group having 1 to 6 carbon atoms, andthe dotted line stands for a further carbon-carbon bond or hydrogen atoms in the 3- and 4-positions of the ring,and salts and cyclic amides thereof.The new compounds possess valuable pharmaceutical activities, more particularly, are potent diuretic, antiasthmatic, hypotensive and antiinflammatory agents. Thus another aspect of the invention is a pharmaceutical composition which comprises as active ingredient a pharmaceutically effective amount of at least one compound of the general formula (I) with at least one pharmaceutically inert carrier or diluent. The invention also relates to a process for preparing these compounds.