Hydroxyindole-3-carboxylic acid amide compounds of the general formula: ##STR1## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are, the same or different, respectively a hydrogen atom, an alkyl group, an aryl group, an aralkyl group or a heteroaryl group, or R.sup.1 and R.sup.2 and/or R.sup.3 and R.sup.4 are respectively groups which are combined to each other taken together with the adjacent nitrogen atom to form a heterocyclic group, R.sup.5 is an alkyl group, R.sup.6 is a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group and X is a hydrogen atom, a halogen atom or a lower alkanoyl group, or their acid addition salts.These compounds are of use as diuretics or a therapeutic medicine for circulation system diseases.