A HIGH-TEMPERATURE X-ray diffractometer has been used to investigate a suggestion by S. B. Austerman (private communication) that there was a reversible phase transition in beryllia at 2,050° C. By this means evidence has been obtained of a new phase appearing at 2,080 ± 50° C. on heating, which reverted to the usual hexagonal beryllia structure at 1,980 ± 50° C. on cooling. In each case the phase-change took place over some 30° C.