Magnetic Penetration Depth of YBa sub 2 Cu sub 3 O sub 7.

A recent paper by L. Krusin-Elbaum, R. L. Greene, F. Holtzberg, A. P. Malozemoff, and Y. Yesherun [Phys. Rev. Lett. 62, 217 (1989)] on magnetic penetration length lambda measurements in YBa sub 2 Cu sub 3 O sub 7 crystals is criticized. It is shown that analysis of temperature-dependent dc susceptibility data is particularly sensitive to the choice of baseline, thus bringing into question the procedures used in arriving at conclusions about the BCS temperature dependence of lambda and its zero temperature value.