In sequential diagnostic reasoning multiple pieces of information have to be combined to find a best explanation for observed symptoms (e.g., Johnson & Krems, 2001). Tracking memory processes involved in reasoning proves difficult because they proceed without accompanying actions towards the environment. However, this is important in order to build and test cognitive models (Schulte-Mecklenbeck, Kühberger, & Ranyard, 2011). Memory indexing is a novel method to study the time course of information processing in memory during reasoning and decision making (Jahn & Braatz, 2014; Renkewitz & Jahn, 2012) by recording eye movements. The basic principle underlying memory indexing is that people look at an emptied spatial location when retrieving information that has been associated with the spatial location during encoding (e.g., Richardson & Spivey, 2000). We use memory indexing to reveal memory dynamics in sequential diagnostic reasoning in order to test process assumptions derived from cognitive models on reasoning and belief updating.