During stereotactic brain tumor biopsies, the detection of protoporphyrin IX (PpIX) fluorescence and microvascular perfusion using laser Doppler flowmetry (LDF) with a handheld fiber optic probe allows the identification of tumor tissue while decreasing the risk of intracranial hemorrhage. Neurosurgeons performing this procedure usually view the measurement values on a screen. When their visual focus is directed at the surgical site, they require an assistant to verbally relay the values. An auditory and visual user interface (UI), which displays measurement values accurately and allows fast and intuitive signal recognition, can improve this procedure. This paper experimentally evaluates an auditory and visual UI for providing real-time measurement feedback during stereotactic brain tumor biopsies. In a user study (n = 15), the accuracy of auditory and visual response was determined using function response tests, and user acceptance was evaluated. The auditory signals proved to be intuitive and easy to recognize and remember. The visual display of measurement values was easy to understand and facilitated the user's decision-making process. Moreover, the UI exhibited high user acceptance.