A method and an apparatus for determining the particle content of a particle stream using a source of light and two receivers arranged offset from one another in the flow direction of the particle stream. The receivers provide an electrical signal to an evaluation unit as a function of the radiation intensity which they receive, and this signal makes possible a determination of the flow velocity and particle size. Coincident passage of two particles is indicated by a pulse occurring in the signal due to a “roof collapse” in the pulse caused by a weakening of the radiation intensity as the particles pass a receiver.