The present invention is concerned with proteins selected from the members of the TGF-.beta. superfamily, which are monomeric due to substitution or deletion of a cysteine which is responsible for dimer formation. The invention is also concerned with nucleic acids, encoding such monomeric proteins, vectors or host cells containing the nucleic acids as well as with pharmaceutical compositions comprising the proteins or nucleic acids encoding the proteins. The compositions can be applied advantageously for all indications for which the respective dimeric proteins are useful.