The invention relates to a combination of protamine with an insulin salt. The insulin salt is derived by crystallization of insulin in the presence of ions of an alkali metal or metalloid such as sodium, potassium, lithium, cesium or ammonium at an alkaline pH range. The protamine is present in an amount from about 0.2 to about 1.5 mg. of protamine for each 100 units of insulin. The insulin salt and protamine form an insoluble complex at a pH from 6.5 to 8 in an aqueous medium, which complex when dried is easily reconstituted without activity loss.