1. The primary structure of human corticotrophin-releasing hormone precursor (h pre-proCRH) has been analysed using a number of computer algorithms to identify the areas of highest predicted antigenicity. 2. These results were correlated with crossreactivity data obtained from studies of antibodies produced in rabbits by immunizing with h pre-proCRH, and a number of related peptides. 3. Six areas of high predicted antigenicity were identified in h pre-proCRH by the prediction routines utilized. Two of these corresponded almost exactly to the two putative cleavage sites of the prohormone, and a third lay within the C-terminal region of one of the products of post-translational processing of the prohormone, i.e. CRH(1-41). 4. Experimental crossreactivity data also indicated that a number of structural factors (e.g. Omega loops, peptide conformation) may also be involved in recognition of peptide fragments by antibodies.