THE SECOND INTERNATIONAL STANDARD FOR CHORIONIC GONADOTROPHIN.

As stocks of the first International Standard for Chorionic Gonadotrophin were running low, the WHO Expert Committee on Biological Standardization authorized the National Institute for Medical Research, London, in 1960 to proceed with arrangements to replace it. This paper describes the nature and handling of the proposed replacement material, its assay by nine laboratories in six countries, and its establishment as the second International Standard for Chorionic Gonadotrophin, with a defined potency of 5300 International Units per ampoule. The International Unit of Chorionic Gonadotrophin is defined as the activity contained in 0.001279 mg of the second International Standard.