Early and accurate detection of emboli is important for monitoring of preventive therapy in stroke-prone patients. An embolic signal caused by emboli can be detected by Doppler ultrasound. Embolic signals are highly non- stationary and last only for a short time. Advanced processing methods are required to distinguish these signals from Doppler signals arising from red blood cells and artifacts. Any detection method involving change detection must rely on determination of an appropriate threshold. In this paper, an adaptive threshold determination method based on discrete wavelet transform (DWT) and statistical properties of the data under investigation is described. The results reveal that the proposed adaptive threshold results in a robust embolic signal detection system.