The invention relates to transparent, autoclavable, non-cytotoxic, essentially compact polyurethane embedding compositions which are prepared by reactinga) modified diphenylmethane diisocyanates withb) compounds with at least two reactive hydrogens, which contain or are composed ofb1) at least one polyether-polyol with an average functionality of from 3 to 8, a hydroxyl number of from 200 to 1000 and an alkali metal ion content of from 150 to 1200 ppm or, preferably, a mixture of (b1) and castor oil and/or at least one polyetherpolyol (b2) with a functionality of from 2 to 3, a hydroxyl number of from 90 to 200 and an alkali metal ion content of less than 10 ppm in the presence or absence ofc) catalysts and to a process for preparing the polyurethane embedding compositions and to the use thereof for articles used in medicine.