Improved compositions and methods are provided for stabilizing a solution of bone morphogenetic protein. The compositions comprise an aqueous solution of GDF-5 and a biocompatible acid, such as hydrochloric, acetic, phosphoric, or trifluoroacetic acid, wherein the solution has a pH of from about 3.0 to about 3.6, thereby providing for improved stability of the GDF-5 protein during handling and prolonged storage at reduced temperatures.