The invention relates to a composition which is polymerizable by ring-opening metathesis polymerization (ROMP) comprising at least one monomer that is polymerizable by ROMP, at least one initiator of the Hoveyda-Grubbs type for initiating the ROMP and at least one retarder selected from the group consisting of heterocyclic a means having a ring with at least one N-atom and four or less other atoms constituting the ring bearing the at least one N-atom. The invention further relates to a process for the preparation of a composition which is polymerizable by ROMP, a dental material obtainable by polymerizing a composition according to the invention and the use of a substance selected from the group consisting of heterocyclic amines having a ring with at least one N-atom and five or less atoms constituting the ring bearing the at least one N-atom or of a mixture of two or more of such substances as a retarder in ROMP.
