The SNB implements its monetary policy by steering short-term interest rates, particularly SARON, close to the SNB policy rate. Doing so requires the SNB to control the provision of reserves. In this Economic Note, we quantify how SARON reacts to adjustments in reserves and show that the relationship can vary over time. In the current environment, SARON decreases by 0.1 basis points if reserves increase by CHF 10 billion.