Four methods were tried in order to reduce the growth of granulation tissue on the dura. The best results were obtained using white petrolatum jelly, which almost completely suppressed the growth of granulation tissue when the recording chamber was filled with petrolatum. Collagen and acrylic seals were very effective in one monkey. Panalog ointment slowed the growth of granulation tissue; preformed silicon sheets had no apparent effect. We conclude that long-term application of petrolatum jelly has no adverse effects and achieves striking suppression of the growth of granulation tissue.