The present Comment addresses two concerns. First, we are concerned that our published work has been cited by Eggert, Goettel, and Silvera [Phys. Rev. B 40, 5724 (1989)] in a manner that might lead the reader to suppose incorrectly that we agree with reports of pressures in the range of 460-550 GPa in a diamond-anvil cell based on ruby-fluorescence measurements. Second, our experience suggests that there is the possibility of misinterpreting fluorescence data at ultrahigh pressures that should be emphasized to the reader. We assert that there is insufficient evidence to support claims that the ruby-fluorescence technique has been used successfully at pressures above about 200 GPa. © 1990 The American Physical Society.