Amelogenesis imperfecta is a hereditary disease of the enamel that is unassociated with generalized defects. Cases of the condition are clinically classified into three groups: hypoplastic, hypomaturation, and hypocalcified. In this study, soluble protein fractions of the enamel from three patients with hypocalcified amelogenesis imperfecta were examined through the use of immunochemical and biochemical techniques. In immunochemical analyses done with a polyclonal anti-amelogenin antibody, all samples from enamel in which there was amelogenesis imperfecta were found to contain considerable amounts of amelogenin peptides. When an enamel sample from one patient was examined by Western-blot transfer and immunobinding analysis, the amelogenin fraction was found to consist of a 26-kDa molecule thought to be normally present in the outer layer of secretory-stage enamel. This enamel was also found to contain albumin as one of the major constituents of the protein fraction. These results suggest that hypocalcified amelogenesis imperfecta may in part be caused by a disturbance in matrix protein degradation during the maturation phase.