The present invention relates to sulfanilide derivatives of formula (I), in which R.sup.1 and R.sup.2 are optionally substituted aryl and heteroaryl groups and the other variables are as defined in the claims, for use as pharmaceutically active compounds, as well as pharmaceutical formulations containing such sulfanilide derivatives. Said derivatives are useful in the treatment and/or prevention of preterm labor, premature birth, dysmenorrhea, inappropriate secretion of vasopressin, congestive heart failure, arterial hypertension, liver cirrhosis, nephrotic syndrome and ocular hypertension. In particular, the present invention is related to sulfanilide derivatives displaying a substantial modulatory, in particular antagonistic activity, of the oxytocin and/or vasopressin receptor. More preferably, said compounds are useful in the treatment and/or prevention of disease states mediated by oxytocin and/or vasopressin, including preterm labor, premature birth, dysmenorrhea, inappropriate secretion of vasopressin, congestive heart failure, arterial hypertension, liver cirrhosis, nephrotic syndrome and ocular hypertension. The present invention is furthermore related to novel sulfanilide derivatives as well as to methods of their preparation.