The recent development of bi‐dimensional detectors operating in the mid‐infrared has opened new possibilities for the observation and analysis of the high mass loss processes in the last stages of stellar evolution. Radio (CO) and maser (OH) observations show that an important roˆle is played by intermediate and low mass stars (1–8 M⊙) in the TP‐AGB phase, and by their circumstellar envelopes of gas and dust. We analyze the problem of characterizing the chemical nature of the AGB envelopes (C‐rich or O‐rich) through mid‐infrared observations by means of a suitable photometric system. ©1995 American Institute of Physics.