Some amino acids and oligopeptides have been used as ligands for Rh(CO)(2)(acac) in the aqueous biphasic hydroformylation of styrene. In particular, the amino acid L-cysteine, that presents a thiolic function, showed to be a good ligand for the rhodium carbonyl complex: in fact, the water soluble catalytic system maintained its activity practically unchanged during three recycled experiments. Also the oligopeptide glutathione in its reduced form gave good performances and the catalytic system obtained by coordination to the rhodium carbonyl showed a good activity in the aqueous biphasic hydroformylation. When other bioligands not containing the SH moiety, as L-tryptophan, L-methionine, L-cystine and vancomycin, have been used to coordinate the rhodiurn atom of the catalytic precursor a pronounced metal leaching occurred so preventing the possibility of recycling the aqueous catalytic phase. (c) 2007 Elsevier B.V. All rights reserved.