Abstract: The present invention relates to pharmaceutical formulations comprising insulin, an insulin analog, an insulin derivative, or a combination of any of the foregoing, and a salt of protamine, to methods of preparing such formulations, and to uses of such formulations in the treatment of diseases and conditions for which use of the insulin peptide(s) contained in such formulations is indicated. The present invention further relates to methods for increasing the stability and/or solubility of insulin in insulin-containing formulations at a pH less than 7.0 by adding a salt of protamine to the insulin-containing formulations.