Abstract: The invention relates to a method for determining the activity of the parasympathetic nervous system or of the sympathetic nervous system of the autonomic nervous system of a living being, in particular a human being, wherein a feature of the condition of the living being is determined, and the activity is determined from the feature of the condition. According to the invention, the activity of the parasympathetic nervous system and/or of the sympathetic nervous system is determined dependent on time. Advantageously, the feature of the condition is a series of heartbeats of the living being, and the activity is determined by analyzing the time intervals between the heartbeats. For this purpose, the heart rate of the living being is preferably measured, and the heartbeat is determined using first positive deflections of a ventricular stimulus (R deflection). The invention further relates to a device for carrying out the method.