The effect of stimulus familiarity on the comprehension of polar adjectives by preschool children was examined by administering a perceptual judgment task. The children's ability to indicate the correct object illustrating a particular word was assessed. Antonyms representing opposite dimensions of quantity, height, length, or size were presented. Although the overall level of performance was highly accurate, the number of correct responses varied significantly as a function of a word's polarity, and dimension tested, and the familiarity of the test objects. Even though preschoolers are usually reported to respond to the marked forms of polar adjectives as if they meant the same as the unmarked forms, such asymmetry in comprehension was found to be largest for the quantity dimension and to occur primarily on the unfamiliar test materials. The findings suggest that: (1) children's initial understanding of such terms may be situation specific; and (2) their asymmetry in performance may reflect a failure to apply existing cognitive structures in new situations. (Author/MV)