Pseudoxanthoma elasticum (PXE) is a connective tissue inherited disease characterized by dermal alterations and mineralization of the elastin fibres. To investigate its pathogenesis, which is still unknown, antibodies against the principal connective tissue components were assayed on ultrathin sections of dermis from 7 PXE subjects and 5 age matched controls. Both control and PXE elastin fibres were positive for heparan, dermatan and chondroitin 0-sulphates, decorin and biglycan. In PXE, elastin fibres were also highly positive for chondroitin 6-sulphate, vitronectin, fibronectin and serum amyloid antigen. Vitronectin and fibronectin were mostly concentrated in the areas of dense mineralization within the elastin fibres. The abnormal microfilament aggregates, often seen in PXE dermis, were positive for all the above mentioned molecular species as well as for collagen types I and III and fibrillin; on the contrary, they were always negative for elastin. The results suggest that PXE is a complex disorder, in which the whole extracellular matrix is deeply disturbed. Therefore, without excluding an elastin gene defect, the data seem rather to suggest that PXE is a disorder of the mechanisms controlling the production of matrix constituents and that elastin mineralization is caused by molecules abnormally produced and entrapped within the fibre during elastin fibrogenesis.