A modulated differential scanning calorimeter ("MDSC") wherein the temperature of the sample and/or the reference is modulated by modulating the characteristics of a gas in thermal contact with the sample and or a reference. In a first embodiment, the major heat flow path between the sample/reference and the furnace is the purge gas in the furnace chamber. The composition of the purge gas in the furnace chamber of the DSC cell is modulated by alternately purging the DSC cell with a high thermal conductivity gas (e.g., helium) and with a low thermal conductivity gas (e.g., nitrogen), thus modulating the flow of heat to and from the cell. In a second embodiment, the sample and reference are heated (or cooled) by a temperature-controlling gas flowing around the sample and reference holders. The gas is heated by being passed through a furnace before it flows around the sample and the reference. The flow-rate of the temperature-controlling gas is modulated, thus modulating the temperature of the sample and the reference. The third embodiment is similar to the second embodiment, but in the third embodiment, the temperature (not the flow-rate) of the temperature-controlling gas is modulated. The third embodiment preferably uses modulation furnaces which have a relatively low thermal mass, such that the sample/reference temperature can be modulated at relatively high modulation rates.