Because of histochemical similarities, there is reason for thinking that some component or components of PSX material are also present in zonular fibers. Since the zonule is a member of the elastic microfibrillar system, PSX material on the lens capsule was tested for immunologic affinity to elastic MFP from three widely divergent sources, using an indirect immunoperoxidase electron microscopic method. Positive staining was obtained with all three antibodies on all components of lens PSX material, including the superficial aggregates, deep fibrogranular zone, and capsular inclusions. The results support our hypothesis that PSX material derives from abnormal polymerization of glycoprotein associated with the zonular-elastic microfibrillar system. Similar staining of the abnormal material within the lens capsule indicates that the lens epithelial cell is involved in processing this protein. It might be suspected that other microfibrillar-secreting cells, even beyond the present range of suspected sources, could produce similar material.