There is considerable interest in the interplay, of superconductivity and magnetism in La2CuO4. Several groups [1–3] have noted signs of superconductivity in nominal La2CuO4, and antiferromagnetism has been reported in La2CuO4-y with y>0. The superconductivity previously reported was of a filamentary nature because although resistance drops to near zero were observed, only small Meissner effects (∼10-3 to 10-4 of perfect diamagnetism) were observed. In this paper we describe our studies of. ceramic samples of La2CuO4-y, loaded with oxygen by high pressure. This technique results in substantial incorporation of O2 in the material (of the order of 0.3 to 0.4% by weight) and in gross changes in the bulk resistivity and magnetization as well as discernable changes in the lattice parameters of the material.