Studies on MTl2 Sr2 Ca2 Cu3 Oy (M = Rare Earth, Y, Sc, Pb, Bi and Th) show that superconductivity in the range 40-77K can be achieved in this system depending on the M-ion. The minimum amount of rare earth required to show a Tc ∼ 70K appears to be 25 mole percent. X-ray studies confirm the single phase material responsible for high Tc superconductivity to be 1212 type. It appears that Pb, Bi and Th substitute at the Tl- site whereas the rare earths, Y and Sc prefer the Ca- site. © 1990.