A new performance index for atmospheric lidar, namely the power-aperture-mixing ratio-scattering cross-section (PAMS) product, is proposed. Unlike the index widely used at present, namely the power-aperture (PA) product, the new index provides an accurate comparison between different types of lidar for measuring the same atmospheric parameters. Using a sodium resonance lidar and a 'Rayleigh' lidar for measuring temperature and wind in the mesopause region (80-105 km) as an example, the concept and application of PAMS are illustrated.