An immature enamel fraction, as far as possible without cells, was prepared from fetal bovine molars, using aqueous-density fractionation. Portions were incubated at 37 degrees C with or without protease inhibitors. Amelogenins and enamelins were then examined for their molecular weight using HPLC-gel permeation. Degradation of amelogenins occurred rapidly and appeared to be related to proteolytic activity, probably localized extra-cellularly. Enamelins remained almost stable over the time intervals used.