The melting endotherm of alpha-form crystallites in wool keratin appears often to be bimodal. The origin of the bimodal endotherm has been considered to correspond to the differential melting of the alpha-form crystallites in the domains of ortho- and paracortical cells. An alternative interpretation is presented, in which the bimodal peak arises from the overlapping of the melting endotherm of alpha-form crystallites and the thermal degradation of other wool histological components.