This invention relates to storage-stable, liquid, partially trimerized and allophanized polyisocyanates having an NCO group content of 15 to 41% by weight, and comprising 5 to 85% by weight of toluene diisocyanate, 5 to 85% by weight of a polyisocyanate of the diphenyl-methane series and an organic compound or mixture thereof. The present invention also relates to a process for the preparation of the storage-stable, liquid, partially trimerized and allophanized polyisocyanates; to storage-stable, liquid urethane prepolymers of these partially trimerized and allophanized polyisocyanates; and to a process for the production of these storage-stable, liquid, urethane prepolymers.