The present invention provides assays for the study of the interaction of EPF and its EPF-related peptides with a hDRR receptor. The assays are useful to identify whether a test compound can bind to the hDRR receptor under conditions in which EPF or related peptide can bind to the receptor. The assays are also useful to determine whether the test compound is an agonist or antagonist of hDRRs. The above assays can be performed in a variety of formats including competitive, non-competitive and comparative assays in which the interaction of EPF or EPF-related peptides with hDRRs is assessed as a positive or negative control or compared to the results obtained with the test compound.