The use of fiber-optic backscattering sensors for inline monitoring of the particle concentration in highly filled dispersions and lacquer systems is shown. Through the miniaturization of the distance between transmitter and detection fiber to < 600 mu m, the light can also permeate high disperse phase fractions of up to 60 %. Due to the measurement setup, both transmission and scattering effects can be found in the resulting signal. The possible mathematical description of the resulting nonlinear measured curve using a simplified model follows.