I.r. spectra of a series of cholesterol gallstones are given and discussed in order to identify the different forms of cholesterol, anhydrous, monohydrate, form II (these forms have recently been characterized spectroscopically by us) and to reveal the other components associated with them in gallstones. It was also revealed spectroscopically that the main component in the gallstones examined was cholesterol monohydrate generally in association with organic (bilirubinate, palmitate) calcium salts. The findings exposed in this paper are consistent with a structural model for cholesterol gallstones given by us in a previous report and suggest at the same time a possible mechanism for their solubilization.