The O2(1Δg) dayglow produced at 1.27 μm by ozone photolysis is ideal for ground-based mapping of high-altitude ozone using long-slit high-resolution spectrographs like CSHELL, CGS4, and Phoenix. Coupled to mapping H2O at 1.13 μm and CO and CO2 at 1.57 μm with the same instruments, it is possible to map hygropause using the rotational temperatures of CO2 and O2(1Δg). Strong seasonal variations of hygropause (from 10 to 40 km) and associated variations of high-altitude ozone (by an order of magnitude above 20 km) are important novel concepts which may be studied in detail by these observations. Showing even greater promise is the combination of O2(1Δg) dayglow mapping with mapping of water abundance and temperature profiles by the thermal emission spectrometer onboard the Mars Global Surveyor. A list of problems which may be solved or improved upon by these observations is included.¿ 1997 American Geophysical Union