The invention relates to a method for determining the presence of an analyte by means of a distribution of small magnetic particles. According to said method, the magnetizations of the small particles are oriented in relation to each other by means of an outer magnetic focusing field； once the focussing field has been terminated, the magnetizations of the small particles are rotated asynchronously to the magnetic field by means of an outer magnetic field of suitable field intensity and rotational frequency, which rotates about a longitudinal axis (z)； the temporal course of the superpositioned transverse magnetization of the set of particles is detected； and the presence of the analyte is deduced from the detected temporal course. The invention also relates to a corresponding device (1).
