Abstract: The invention relates to transparent, substantially compact polyurethane casting compositions, sterilizable with superheated steam, which are prepared by the reaction of:A) modified diphenylmethane diisocyanates (A) that are liquid at 23.degree. C. and are in turn are obtained by the reaction of1) a diphenylmethane diisocyanate isomer mixture, which in terms of 100 parts by weight comprises 60 to 90 parts by weight of 4,4'-diphenylmethane diisocyanate, 40 to 8 parts by weight of 2,4'-diphenylmethane diisocyanate, and 0 to 5 parts by weight of 2,2'-diphenylmethane diisocyanate with2) at least one polyoxypropylene polyol initiated with glycerine and/or trimethylol propane, having a molecular weight of 350 to 800 with a ratio of NCO:OH groups of 2.5:1 to 15:1, withB) at least one compound having at least two reactive hydrogen atoms in the presence or absence ofC) catalysts,as well as to a process for preparing the polyurethane casting compounds and their use for medical-technical articles.