A process for regenerating a water-soluble hydroformylation catalyst system comprising a coupler rhodium hydrogen-carbonyl complex of rhodium and compounds of the formula ##STR1## wherein Ar.sup.1 and Ar.sup.2 and Ar.sup.3 are individually phenyl or naphthyl, Y.sup.1, Y.sup.2 and Y.sup.3 are individually selected from the group consisting of alkyl and alkoxy of 1 to 4 carbon atoms, halogen, --OH, --CN, --NO.sub.2 and R.sup.1 R.sup.2 N--, R.sup.1 and R.sup.2 are individually alkyl of 1 to 4 carbon atoms, X.sup.1, X.sup.2 and X.sup.3 are individually carboxylate (--COO.sup.-) or sulfonate (--SO.sub.3.sup.-), m.sub.1, m.sub.2 and m.sub.3 are individually integers of 0 to 3, at least one of m.sub.1, m.sub.2 or m.sub.3 being equal to or greater than 1, and n.sub.1, n.sub.2 and n.sub.3 are individually integers of 0 to 5 and if appropriate in excess comprising adding maleic acid, fumaric acid or olefinically unsaturated compounds of formula ##STR2## wherein X is selected from the group consisting of O, S, -- ##STR3## or ##STR4## and R.sup.3, R.sup.4 and R.sup.5 are individually hydrogen, or alkyl or aryl to an aqueous solution of the catalyst system in an amount sufficient to remove sulfonated or carboxylated alkyl-arylphosphanes.