Biological standards and pharmacopoeias.

The use of standards in the control of biological substances is of particular importance because the potency of such substances cannot be adequately determined by physical or chemical means. For these substances, therefore, it is necessary to compare the activity or potency of a given quantity with that of a similar quantity of a standard or reference preparation to which a unitage has been assigned. In order to eliminate as far as possible the inherent variables in biological tests, especially in tests involving animals, the comparison between the standard and the unknown must be made in a single test. Furthermore it is essential that the biological activity of the standard has the same properties as those products for which the standard is used as a control. The master standards are the International Standards held by the World Health Organization and it is necessary to establish European or National Standards calibrated in International Units in order to conserve the stocks of the master standards. Criteria for the quality of preparations suitable as standards will be considered and some examples of their use will be presented.