We identify a disorder induced mobility edge E c in the system Bi-2212+Y/Ca. The ~uhstitution shifts the Fermi energy below E c and causes a superconductor-insulator transition. In the insulating state charge transport happens by Variable-Range-Hopping (Shklovski-Efros case). The transition can either be reached by y3+ or Ce 4+ substitution and depends only on the total carrier density. The Metal-Insulator-Transition (MIT) is a common feature of all high temperature superconductors (HTSC) and has attracted much attention 1'2. It is usually achieved by substituting a cation with lower valence into the insulating parent compound (Sr2+/La 3+ in La2CuO4, Ca2+/Y 3+ in Bi2Sr2YCu208). This creates hole like states at the Fermi energy E F that can transport electrical charge. This transport is characterised by puT as is predicted for free electrons with coupling to Debye-phonons and observed in ordinary metals such as Cu. Therefore HTSC are often called "metallic" although the origin of the linear temperature dependence is not yet known. The phase diagram of Bi-2212 + Y/Ca is shown in Figure 1. As in all other HTSC one observes a "metallic" and superconducting phase neighbouring an insulating ( p(T-*0, w-*0)=oo ) and antiferromagnetie phase. The superconducting phase exists 700 t Bia~lrz(Cal-zYt)CuzOs*;f