SUMMARY Within a Human Information Processing (HIP) framework, dreaming can be subdivided into three main components: Input, Processing and Output. Until recently, only the Output has been extensively studied due to its relatively easy accessibility in the form of dream reports. Much less is known about the other two components.A method is presented by which one can get information on the nature of the input component to dream processing. In this method the subjects are requested to identify the memory sources of their dreams, collected upon experimental awakenings. The materials thus obtained are then classified into categories derived from Tulving's distinction between Episodic and Semantic memory. Several aspects, including interviewing and scoring procedures, had to be specified in order to use the method, which was applied in a series of studies. The aim was to clarify the similarities as well as the differences between REM and NREM dreams. The main results give further support to the hypothesis of the existence of a unique dream production system that operates at different levels of engagement during the various sleep phase