Abstract: The present disclosure relates to multi-specific molecules which are capable of simultaneously binding at least two different target antigens or epitopes. The molecules comprise at least one binding domain molecule (BDM) which hinds to a first target antigen or epitope, the BDM being modified for selective binding to a heterologous target, coupled to a pharmacologically active protein or peptide which is an antibody or antigen-binding fragment thereof or a non-antibody protein or peptide which binds to a second target antigen or epitope, the BDMs being coupled to a C-terminus of a polypeptide present within the pharmacologically active protein or peptide.