Polyimide (PMDA-ODA) films were analyzed by mass spectroscopy to determine their high-temperature stability. Using a high-resolution instrument, the identity of the low-molecular-weight evolved gases was confirmed. With a semiquantitative technique, the effect of a vacuum pre-bake was shown to reduce outgassing appreciably during subsequent treatment at high temperature. Subjection of the films to moisture did not affect their thermal stability. Low-temperature processing (240°C vs 400°C) reduced gaseous evolution by an order of magnitude.