Silicone oil was injected into 23 rabbit eyes, which had undergone vitrectomy and which were then examined in the electron microscope six weeks later. Retinal lesions were observed in the outer plexiform layer. They consisted mainly of a subtotal disappearance of the processes of horizontal and bipolar cells and of the synaptic terminals of the photoreceptors. The lesions were seen only in areas of the retina that had been in permanent contact with the oil bubble. They did not depend on the purity of the silicone oil injected.