Why do we lose, or have trouble accessing, an idea that was in the focus of attention only a moment ago, especially in the absence of any apparent distraction? We tested the hypothesis that accessing a single item that is already active is affected by implicit interference (interference of which we have little or no awareness). We presented masked words that were semantically related or unrelated to a single visible target word that participants were cued to think of ("refresh") a half second after its offset. Masked related but not unrelated words increased time to refresh the target but did not influence time required to read a target that was physically present. These findings provide novel evidence that an item in the focus of attention is subject to semantic interference. We suggest that such implicit semantic interference may contribute to the common "lost thought" experience and to cognitive deficits in populations in which refreshing is impaired. (Contains 2 figures and 1 footnote.)