This invention relates to storage-stable, liquid, partially trimerized polyisocyanates having an NCO group content of 24 to 40% by weight, and comprising 20 to 88% by weight of toluene diisocyanate and 12 to 80% by weight of a polyisocyanate of the diphenylmethane series. The present invention also relates to a process for the preparation of the storage-stable, liquid, partially trimerized polyisocyanates; to storage-stable, liquid urethane prepolymers of these partially trimerized polyisocyanates; and to a process for the production of these storage-stable, liquid, urethane prepolymers.