[en] A graphical method is described that allows the determination of specific radioactivities of radioactively labelled hormones. This method combines the self-displacement technique, plotting bound/free ratios versus mass of unlabelled hormone or total radioactivity of labelled preparation added to the receptor preparation, and the maximal binding capacity of the labelled hormone. The procedure presented provides a more realistic specific radioactivity for use in all binding experiments. Application of the method is demonstrated for ¹²⁵I-labelled ovine prolactin, and data are presented for ¹²⁵I-labelled human choriogonadotropin and [³H]testosterone. (author)