The susceptibility of the Defense Mechanism Inventory (Gleser & Ihilevich, 1969) to situational stress variables was evaluated by an experiment where 54 men and 52 women were given half the inventory, then were given word puzzles to solve which were either easy or difficult, and finally given the second half of the inventory. Results showed that the composite measure of defensive style, which contrasts the acting-out defenses from the inward focusing ones, was not affected differentially by the experimental manipulation. The specific defense indices were affected by the experimental manipulation for men but not for women. The composite measure is thus shown to be a basic trait impervious to situational stress, while the specific defenses are seen more as resembling situational states.