Differential scanning calorimetry (DSC) was used to study the effects of cholesterol on the thermotropic phase behavior of fully hydrated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). DPPC was studied with cholesterol ranging from 0 to 22 mol% cholesterol over a temperature range from 20 to 50?C. DSC studies show a decrease in the main transition temperature (Tm) for DPPC with concentrations of cholesterol increasing up to 12 mol%. However, at concentrations greater than 12 mol%, there is an increase in Tm for DPPC. The pre-transition for DPPC was also found to be diminished at cholesterol concentrations greater than 5 mol%.