Abstract: Apparatus for monitoring particulate material in a fluid comprising a passageway (17), through which fluid to be monitored is passed, at least a portion (24) of the boundary of the passageway (17) being translucent to enable radiation to pass through that portion (24). A camera (40) is arranged to receive such radiation and is constructed to generate electrical signals representative of the images it receives. Image analysis means (57) are connected to receive those electrical signals and to provide data from them relating to the particulate material contained within the fluid.