Abstract: A method for screening for osteoporosis comprising bone sialoprotein of mammals. Osteoporosis can be screened by bringing the body fluid sample collected from a living body into contact with the above-mentioned diagnostic agent to immunochemically detect the antibody which is present in the said sample and specifically reacts with the said diagnostic agent.

Abstract: An animal tissue antigen for osteoporotic patients that reacts with antibody in a serum of human osteoporotic patients, but does not react with that in normal human serum. Preferably, a specific antigen for osteoporotic patients in rat or mouse epithelium of tongue mucous membrane, epithelium of tracheal mucous membrane, upper lip epidermis or follicular epithelium containing upper lip hair shafts, or a specific antigen for osteoporotic patients contained in cultured cells of a human squamous cell tongue carcinoma cell lines such as SCC-9 and fibroblast cell lines such as MRC-5. Osteoporosis can be both specifically and easily diagnosed by bringing the above-mentioned antigen in contact with a serum of a subject and then testing for the presence of an antigen-antibody reaction.

Abstract: A method for assaying an immunologically active substance based on the antigen-antibody reaction in a liquid phase, and a reagent for use in the method are disclosed. This method comprises adding a reagent containing a compound represented by the general formulaR.sup.1 O---[(CH.sub.2 CH.sub.2 O).sub.m (AO).sub.n ]--R.sup.2(wherein R.sup.1 and R.sup.2 each represents a hydrogen atom or a hydrocarbyl group containing 1 to 5 carbon atoms, AO represents an oxyalkylene group containing 3 to 4 carbon atoms, m and n represent the number of oxyethylene groups and that of oxyalkylene groups, respectively, with said oxyethylene groups and oxyalkylene groups forming a random copolycondensate and having a molecular weight of 1000 to 20000, and the ratio of m/n being 60/40 to 90/10).