  Our paper on the isotope effect in high-temperature superconductors with
cation substitutions presents a comprehensive analysis rooted completely in the
experimental evidence. In this Reply we show that pair-breaking disorder,
isotope effects, doping-induced variations in Tc and in the magnetic
penetration depth, Coulomb's law, and Anderson's theorem are treated with
correct physical and mathematical fundamentals. In contrast, the theory
fostered in the Comment by Alexandrov and Zhao contradicts several specific
experimental facts, eight of which are briefly discussed. Their Comment also
uncritically repeats a previously discredited assertion of an isotope effect in
the superconducting carrier mass, incorrectly assumes that cation doping
continuously varies intrinsic superconducting parameters, unjustifiably assigns
importance to data from samples with serious quality problems, and renders a
false estimate of the pair-breaking strength.
