Capabilities of lidar systems operating in the middle IR spectral region are examined. The utility of the CO2-laser first and second harmonic and sum frequency generation for lidar sounding of atmospheric water vapor and carbon monoxide concentrations by the DIAL technique is discussed. The absorption lines of H2O and CO most useful for remote gas analysis are listed. The results obtained from numerical simulation of ground-based and airborne lidar sensing of the atmosphere along horizontal and vertical paths are presented.