A method of modifying protein solubility employs polyionic polymers. These facilitate
the solubilization, formulation, purification and refolding of proteins especially
incorrectly folded proteins and aggregated proteins. Compositions are described
that are suitable for formulating TFPI. The compositions allow preparation of pharmaceutically
acceptable compositions of TFPI at concentrations above 0.2 mg/mL and above 10 mg/mL.