By using monkey eyes and light microscopy, transmission electron microscopy and scanning electron microscopy we have studied the role of platelets in Schlemm's canal. In eyes connected to a reservoir and subjected to an elevated intraocular pressure, there was break-down of the cell membranes facing the invaginations into the endothelial cells, resulting in local protrusions from the invaginations and ruptures. Other unphysiological openings in the inner wall were due to separation of the intercellular junctions. Aggregates of platelets were observed at both these types of openings. Small aggregates were observed also in massaged eyes and in eyes which had not been touched before fixation. It seems likely that the intercellular junctions are fragile, tending to disrupt even under normal conditions and that platelets play a role in their repair. It is also suggested that platelets tend to restrict the size of the physiological pores.