Abstract: An in vitro method of evaluating the antagonistic versus agonistic effects of a receptor-binding test substance on a selected type of cells containing endogenous intra-cellular hormone receptors, is disclosed. Said test substance, and separately a reference substance, known to be either an antagonist or an agonist, are incubated with said selected type of cells, and the magnitude of the selected cellular response resulting from hormone/receptor interaction, is analyzed. In case the method is performed on at least two selected types of cells which derive from different kinds of tissues, it is possible to evaluate the pattern of antagonistic versus agonistic effects of the selected test substance on said kinds of tissues.