Interfacial interactions between bile salt solutions, sodium cholate (NaC), sodium deoxycholate (NaDC), and sodium chenodeoxycholate (NaCDC) (in the concentration range 5 X 10(-5) to 5 X 10(-2) M), and the cholesterol surface (both bare and precontacted with bile salt solutions) are evaluated on the basis of the knowledge of the surface free energy components of both cholesterol and bile salt solutions. By use of these components, the contact angles are estimated and compared to experimental ones. It was found that large changes in the wettability of the cholesterol surface took place when the surface was in contact with solutions in which micelles were present. Calculations suggest that micelles adsorbed on the cholesterol surface are hydrated.