It is shown that samples of La2-xSrxCuO4 prepared under 100 bar oxygen pressure exhibit a metallic conductivity which increases as x increases up to x=0.34. In spite of this behavior, superconductivity disappears with Tc decreasing from x=0.15 to x=0.25. This decrease in Tc is shown to be continuous (and not dominated by phase separation). Such decreases in Tc are shown to be a common feature of high temperature superconductors, being observed in YBa2Cu3Oy-like systems as well as in doped Bi 2212 and Tl 1201 compounds. © 1989.