In the traditional conception of working memory for word lists, phonological codes are used primarily, and semantic codes are often discarded or ignored. Yet, other evidence indicates an important role for semantic codes. We carried out a preplanned set of four experiments to determine whether phonological and semantic codes are used similarly or differently. In each trial, random lists of one, two, three, four, six, or eight words were followed by a probe to be judged present in the list or absent from it. Sometimes, a probe was absent from the list but rhymed with a list item (in Experiments 1 and 2) or was a synonym of a list item (in Experiments 3 and 4). A probe that was similar to a list item was to be rejected just like other nontarget probes, a reject-similar use (in Experiments 1 and 3), or it was to be placed in the same category as list items, an accept-similar use (in Experiments 2 and 4). The results were comparable in the accept-similar use of both phonological and semantic codes. However, the reject-similar use was interestingly different. Rejecting rhyming items was more difficult than rejecting control words, as expected, whereas rejecting synonyms was easier than rejecting control words, presumably due to a recall-to-reject process. This effect increased with memory load. We discuss theoretically important differences between the use of phonology and semantics in working memory.