The use of pneumatic pipelines to convey solids is a technique which is now used in many industries where materials have to be moved in bulk. On-line measurement of the solid-gas flow in a pneumatic conveyor is difficult, and commercial instruments are rare. This paper describes a range of existing and experimental systems which can be used to measure the characteristics of solid-gas flow in a lightly loaded pneumatic conveyer. The authors' interpretation of what is meant by light phase is followed by a suggestion of the capabilities that an 'ideal' solids flowmeter should possess. A table of the major types of sensor is presented along with their possible uses. Specific instruments for the on-line measurement of particle size, solids concentration, solids velocity and solids mass flow rate are described. Recent research developments in the use of tomographic methods for concentration profile and velocity profile measurement an also discussed. Finally, the problems still to be overcome in on-line measurement of solid-gas flows are briefly considered.