The Fourth International Standard for insulin.

The composition, analysis and distribution of crystalline insulin for the Fourth International Standard for Insulin is described. In an international collaborative assay 20 laboratories compared this Standard with the Third International Standard, and the statistical analysis of the results is reported.On the basis of the results the Fourth International Standard for Insulin is established with a potency of 24.0 IU/mg. The International Unit is thus defined as the activity contained in 0.04167 mg of the Standard preparation.