The activity of different steroids in producing thymic involution.

The assay method for corticotrophin, in which the involution of the thymus of the nestling rat is measured, can be applied successfully as a quick and simple screening test for biologically active corticosteroids. The sensitivity of the test is such that injection of a standard dose of cortisone acetate produces different results when made up in different media, or injected by different routes. A standard procedure for dispensing and injecting the steroids has therefore been adopted. Of the steroids investigated, it is noticeable that those possessing marked thymolytic activity are also steroids with therapeutic properties.