The specific gravity of fluorosilicone oil (trifluoropropylmethyl siloxane) is greater than that of water, and because of this it opens up new possibilities in vitreoretinal surgery: In cases of PVR detachment, retinal defects at the inferior margin or the posterior pole can be reliably tamponaded. If there is a peripheral retinal hole, the retina is reattached solely by injection of the oil - drainage is unnecessary, since the subretinal fluid is forced back into the vitreous cavity through the retinal defect. Retinal folds resulting from a giant tear will flatten out of their own accord. The present paper communicates initial clinical experience with fluorosilicone oil in 21 eyes (trauma and PVR detachment cases, some of which were considered hopeless). Even though the cases selected for surgery were extreme, reattachment was accomplished intraoperatively in all but one of them. Redetachment occurred in 4 out of 10 eyes following removal of the oil; this was rectified with low-density silicone oil. An immediate side-effect of the new oil was a transient iritis, seen in 5 out of 21 cases. A suspected side-effect after longer-term observation (mean 19 weeks) was that the oil promoted PVR. Out of 4 histologically studied membranes which proliferated under the oil, phagocytosis and foreign body reaction to the oil were found in one of the specimens. No retinal damage due to the oil could be detected by electroretinography. As an intraoperative aid, fluorosilicone oil is thoroughly to be recommended. If a long-term tamponade is essential, the fluorosilicone oil should be replaced with low-density silicone oil (dimethylsiloxane) after a few weeks.