THE SECOND INTERNATIONAL STANDARD FOR PROLACTIN.

In 1953 the WHO Expert Committee on Biological Standardization asked the National Institute for Medical Research, London, to collect and study suitable material to replace the First International Standard for Prolactin, stocks of which were running low. This paper reports the nature and handling of the proposed replacement material, its potency as determined by comparison with the First International Standard by international collaborative assay, and its establishment as the Second International Standard for Prolactin, with a defined potency of 22 International Units per mg. The International Unit of Prolactin is defined as the activity contained in 0.04545 mg of the Second International Standard.