Five patients with recessive pseudoxanthoma elasticum (PXE-R) and four with dominant transmission of the disease (PXE-D) belonging to the same family were studied by light and electron microscopy. In PXE-R, calcification in the elastic fibres causes their enlargement, excavation and fragmentation. On the other hand, in PXE-D irregularly shaped and unevenly lined elastic strands may form an anastomotic wickerwork intimately intermingled with the collagenous texture. In other places, elastic bundles seem to be composed of very tiny elements. Both aspects represent a dysplasia of the elastic tissue. Independently of the mode of inheritance, a variable proportion of enlarged collagen fibrils exhibit a "flower-like" structure. Additionally, in PXE-D alone a peculiar aggregation of small and large collagen fibrils is observed. Granulofilamentous material mixed with tiny collagen fibrils is found in both groups of patients. On the basis of our observations, PXE-R and PXE-D may be identified by light and electron microscopy.