Flame-resistant molding compositions are prepared by adding at least one substance selected from the class consisting of (a) oxides or hydroxides of the rare earth metals, (b) graphite, or (c) precious metals or their compounds or complexes and mixtures of (a), (b) or (c) to a composition containing mixtures of organic polymers other than diorganopolysiloxanes and diorganopolysiloxanes. Although it is not essential, silicon dioxide having a surface area of at least 50 m.sup.2 /g and crosslinking agents may be incorporated in these molding compositions.