Isoquinolines of the formula ##STR1## wherein R.sup.1 is H or alkyl of 1 - 4 carbon atoms, R.sup.2 is H and R.sup.3 is OH or R.sup.2 and R.sup.3 collectively are a C--C bond, and physiologically acceptable acid addition salts thereof have anti-depressant activity and can be prepared by solvolyzing or hydrogenolyzing a compound of the formula ##STR2## or an acid addition salt thereof, wherein R.sup.4 is R.sup.1 or R.sup.6, R.sup.5 is OR.sup.7 or, when R.sup.4 is R.sup.6, R.sup.3 ; R.sup.6 and R.sup.7 are radicals which can be split off solvolytically or hydrogenolytically and R.sup.1 and R.sup.2 are as above; and the optional step of dehydrating a resulting carbinol (R.sup.2 is H, R.sup.3 is OH) and/or treating a resulting compound (R.sup.1 is H) with a N-alkylating agent and/or converting a resulting base to a physiologically acceptable acid addition salt by treatment with and acid.