The invention provides methods for improving the physical and chemical stabilities of therapeutic proteins in solutions by reducing or eliminating protein degradation, aggregation and precipitation using small molecule stabilizing agents such as proline, arginine and/or compounds capable of forming a Schiff bond with amino groups of the protein. The invention further provides liquid formulations of a monomeric insulin stabilized by one of more stabilizing agents such as proline, arginine and/or acetone. Also provided are methods of making and using the stabilized monomeric insulin formulations.
