Stable bulk superconductors in the Tl‐Ca‐Ba‐Cu‐O system with zero resistance up to 125 K are discussed. Structural, magnetic, and electronic transport properties, including thermoelectric power data, are presented on a variety of phases in this system. The anisotropic resistivity of Tl2Ba2CaCu2O8single crystals is discussed. The in‐plane and c‐axis resistivities are ∼7×10−4&OHgr;‐cm and 2×10−1&OHgr;‐cm, respectively, at room temperature. The c‐axis resistivity decreases with decreasing temperature in the temperature range from room temperature down to the superconducting transition temperature, and the second derivative of &rgr;cis negative, unlike that of YBa2Cu3O7and Bi2Sr2.2Ca0.8Cu2O8single crystals. The anisotropic thermopower of Tl2Ba2CaCu2O8single crystals is also described. The room temperature value ofSabis about 14 &mgr;V/K.Sabincreases linearly with decreasing temperature at a rate of 0.06–0.065 &mgr;V/K2down to about 160 K, below whichSabflattens off and drops to zero atTc.Scat room temperature is around 30 &mgr;V/K and depends only weakly on temperature. Conventional scattering mechanisms cannot explain these normal state properties self‐consistently.