Differential scanning calorimetry (DSC) was used to study the effects of isopropanol and n-propanol on the thermotropic phase behavior of dipalmitoyl-phosphatidylcholine (DPPC), a 16-carbon acyl chain phospholipid. Concentrations ranging from 1% to 10% (v/v) of isopropanol and n-propanol were used. Heating and cooling scans over a temperature range of 10? to 50? C were carried out. The inclusion of isopropanol and n-propanol in the bilayer resulted in a biphasic effect on the main transition temperature of DPPC, i.e., low concentrations of isopropanol and n-propanol (up to 2.75%) reduced the gel-to-liquid crystalline phase transition temperature, while higher concentrations of propanols increased these transition temperatures. The gel to rippled-gel pre-transition temperature peaks were found to disappear at propanol concentration higher than 2.75%.