An aqueous formulation for cleaning grease and oil from metal, plastic, glass or other surfaces includes water, a surfactant, and a corrosion-inhibiting amount of a 2-piperazinone. The surfactant is chosen from the class of materials possessing at least some ability in aqueous solution to disperse the grease and oil in an aqueous suspension. The formulation preferably includes both an anionic and a nonionic surfactant. The 2-piperazinone inhibits corrosion of the metal or other surface without unduly reducing the dispersive ability of the surfactant(s). The preferred 2-piperazinones for use in the disclosed invention are 4-(2-hydroxyethyl)-2-piperazinone (4-HEP) and N,N-dimethyl-2-piperazinone (NNDP). The formulation is used by agitation in contact with the surface to be cleaned, for example, by mechanical agitation of the surface, by spraying the formulation against the surface, or by the application of ultrasound waves. A concentrate for preparing the formulation contains the surfactant(s) and 2-piperazinone at a concentration 5 to 20 times their concentrations in the formulation; the concentrate is then diluted with 5 to 20 parts of water to yield the formulation.