The international reference preparation of tylosin.

The Central Veterinary Laboratory, Weybridge, England, was requested by the WHO Expert Committee on Biological Standardization to obtain suitable material for an international reference preparation of tylosin and to arrange a collaborative assay. A batch of 150 g of highly purified tylosin was assayed by ten laboratories in nine countries against the tylosin standard of a commercial manufacturer. On the basis of the results obtained, the material has been established as the International Reference Preparation of Tylosin and the International Unit for Tylosin has been defined as the activity contained in 0.001 mg of the International Reference Preparation of Tylosin.