Initiator system (i) for self-hardening plastics contains: at least one salt (a) of a dialkylbarbituric acid, an alkylcycloalkylbarbituric acid and an alkylarylbarbituric acid and/or a cycloalkylarylbarbituric acid insoluble in methacrylate monomer at least one heavy metal salt (b) insoluble in methacrylate monomer at least one halide-ion donor (c) soluble in methacrylate monomer and at least one acid (d) soluble in methacrylate monomer. An independent claim is included for a bone cement composition comprising component A in the form of paste, composed of at least one methacrylate monomer, at least one polymethylmethacrylate soluble in methacrylate monomer, at least one polymethylmethacrylate insoluble in methacrylate monomer and salts (a) and (b) and a component B in the form of paste, composed of at least one methacrylate monomer, at least one polymethylmethacrylate soluble in methacrylate monomer and at least one polymethylmethacrylate insoluble in methacrylate monomer, (c) and acid (d).
