[en] The preparation and use of charcoal-agar discs for separation of free from antibody-bound steroid in an existing radioimmunoassay protocol is described. This procedure eliminates the centrifugation and decanting operations required when using charcoal-dextran suspension. The disc is more robust and easily handled and much more rapidly prepared than the charcoal-gelatin disc of Saba (1976, J. Endocrinol., 70, 141-6). (author)