Modulated temperature-DSC is a new method for measuring the thermal behaviour of materials. In this method, the response of the sample to a time-dependent signal (sinusoidal temperature change) is measured. Two different methods are known for the evaluation of the measured data. The first is the separation of the measured data into reversing and non-reversing components of heat flow. The second is based on the linear response theory and yields a complex heat capacity with a real part (storage heat capacity) and an imaginary part (loss heat capacity). The theoretical basis and the possibilities of interpretation of both evaluation methods are investigated. The results of both methods are compared theoretically for the case of simple time-dependent processes. Experimental results are given for the glass transition process.