A blood protein (NSILA) which mimics the biological activity of insulin in serum, but is not suppressed by insulin antibodies. During acid-ethanol extraction of Cohn fraction III, 10% of the activity is found in the supernatant (NSILA-S) and the remaining activity in the precipitate (NSILA-P). The latter is a large molecular compound, much less stable than the soluble fraction. NSILA-S is a more potent growth factor than insulin and exhibits sulfation activity.