Negated sentences are known to be more cognitively taxing than positive ones (i.e., "polarity effect"). We present evidence that two factors contribute to the polarity effect in verification tasks: processing the sentence and verifying its truth value. To quantify the relative contribution of each, we used a delayed verification task. The results show that even when participants are given a considerable amount of time for processing the sentence prior to verification, the polarity effect is not entirely eliminated. We suggest that this sustained effect stems from a retained negation-containing representation in working memory.