Descemet's membrane consists of two zones, the 'anterior banded zone' which contains wide-spaced collagen and the amorphous 'posterior non-banded zone'. It is attached anteriorly to the corneal stroma by a narrow transitional zone termed the 'interfacial matrix'. The distribution of fibronectin and P component within the different layers of Descemet's membrane was investigated using an ultrastructural immunogold technique. Seven normal human corneas from an eye bank and one specimen from an orbital exenteration were examined. Fibronectin was predominantly present in the posterior part of the posterior non-banded zone and in the anterior banded zone. The anterior part of the posterior non-banded zone contained less fibronectin. P component was present throughout the anterior banded and posterior non-banded zones. There was a sharp demarcation at the interfacial matrix since neither substance was observed in the corneal stroma. The differences shown in the distribution of fibronectin and P component within Descemet's membrane may have resulted from their binding to other substances or alternatively from differences in the quantities laid down during the evolution of this basement membrane.