Differences in the preferential solubilization of cholesterol and competitive solubilizates (P-sitosterol and aromatic compounds) in bile salt micelles was systematically studied by changing the molar ratio of cholesterol to competitive solubilizates. The cholesterol solubility in a mixed binary system (cholesterol and P-sitosterol) was almost half that of the cholesterol alone system, regardless of the excess-sitosterol quantity added. On the other hand, the mutual solubilities of cholesterol and pyrene were not inhibited by their presence in binary mixed crystals. Finally, the cholesterol solubility was measured by changing the alkyl chain length of n-alkylbenzenes. When tetradecylbenzene was added to the bile solution, the cholesterol solubility decreased slightly and was below the original cholesterol solubility. Based on Gibbs energy change (Delta G degrees) for solubilization, chemicals that inhibit cholesterol solubility in their combined crystal systems showed a larger negative Delta G degrees value than cholesterol alone. (C) 2007 Elsevier Ireland Ltd. All rights reserved.