Lidar observations, depending on the detection of backscatter from a pulse of light by particles along its path, have been used to study chimney plumes and their environment. Important technical improvements to the basic equipment have included the use of swept gain and the development of a brightness modulated display. A number of examples of lidar scans through plumes are presented to demonstrate the value of the improved display. Lidar observations of plumes over periods of about an hour have been used to predict the concentration of pollution at the ground. In neutral conditions, the predictions were significantly better than predictions based only on meteorological data. Observations of the rise and growth of a plume have suggested that, in the equation of motion describing the rise of a plume element, the rate of change of upward momentum should be equated to about one-half rather than the whole of the buoyancy force. Finally, a technique of analysis leading to vertical profiles of aerosol concentration in the lower layers of the atmosphere is outlined. These profiles often reveal features that are vital to a full understanding of plume behaviour.