Contrary to hitherto published results, the authors provided evidence of significant pronucleation activity in the protein fraction which is not linked to concanavaline A. Delipidation or proteolysis markedly reduce the pronucleation activity of this fraction. Albumin was identified as the main protein in this fraction. The lipid-protein complex formed by albumin and lipids had a high pronucleation and crystallization activity in relation to cholesterol. Calcium ions increased the crystalization activity. Complexes formed by proteins and lipids can be vectors of the main pronucleation activity in bile. In investigations of the main cholesterol fraction the authors provided evidence that only part of so-called pronucleation proteins is linked to vesicles--i.e. IgM, IgA and biliary glycoprotein BGP I and II. The authors assume that only proteins firmly linked to vesicles can participate in the process of cholesterol crystallization. Biliary glycoprotein BGP I and II was present in vesicles and when added into a model bile it presented a high pronucleation activity. Biliary glycoprotein is a new hitherto not identified pronucleation protein in bile.